FNA is a well-established technique to procure tissue for diagnosis in patients with unresectable disease and in those patients who may be eligible for therapeutic protocols.⁴ Preoperative biopsy of mass lesions in resectable patients, however, is more controversial.⁵ The potential delay in diagnosis, low negative predictive value and purported increased costs are cited as arguments for resection without confirmation if the clinical diagnosis in straightforward.⁵ Accuracy of the clinical and radiological diagnosis is not 100%,^6–9 however, and the morbidity of pancreatic surgery, although improved over the past 25 years, is still fairly significant especially in the elderly population.¹⁰ In addition, not all malignancies are surgically managed – lymphoma for example – and non-surgical management of patients with pre-malignant disease is increasingly common.^11–14 The accuracy and utility of preoperative FNA is dependent on the quality of the sample as well as the quality of the interpretation. Cytology interpretation requires training in cytological principles and criteria, and most importantly requires experience in pancreatic cytology using a multimodal approach that incorporates the clinical, radiological and ancillary laboratory tests into the overall interpretation of the specimen.^15,16

Unlike other abdominal organs such as the liver and kidney, a core biopsy (CB) of the pancreas is associated with a significant risk of complications. As such, FNA remains the primary means of establishing a tissue diagnosis preoperatively. Before the development of interventional EUS, pancreatic biopsies were performed using either CT or transabdominal US guidance. With the advent of EUS, transgastric or transduodenal FNA of pancreatic masses has provided an alternative procedure for acquiring tissue to confirm the presence of pancreatic cancer and, in many centres, has entirely replaced CT-guided biopsies. It should be recognised, however, that CT is perhaps the most widely used and most important single test used in preoperative staging of pancreatic cancer and in assessment of tumour resectability, and has been shown to be superior to most other imaging modalities in accurately predicting resectability and staging of pancreatic adenocarcinoma.^17,18 Although a recent randomised, prospective crossover trial of EUS-guided FNA versus CT- or US-guided FNA for diagnosing cancer showed no statistically significant difference in the sensitivity or accuracy of CT/US-FNA and EUS-FNA,¹⁹ there are several advantages of an EUS-FNA over percutaneous FNA. Perhaps the greatest advantage is that it allows biopsy of small (0.5 cm) lesions that are not evident by conventional imaging studies.²⁰ The enhanced resolution is, in part, from the proximity of the transducer to the organ examined. The short needle path decreases potential complications as well. The tissue around the needle path is resected at the time of surgery in the typical adenocarcinoma of the pancreatic head, and this reduces the possibility of tumour dissemination. EUS also simultaneously allows for accurate staging of pancreatic malignancy by sampling suspicious peripancreatic nodes and liver lesions. However, both techniques are robust and the eventual choice is dependent on several factors including availability of EUS and local expertise both in procuring and interpreting the FNA sample.

The EUS equipment consists of an image guidance system and the echoendoscope that is placed into the stomach or duodenum (Fig. 10.1). Using the guidance of the high-frequency ultrasound transducer on the tip of the echoendoscope, a small 19–25 gauge needle is passed through the wall of the gastrointestinal tract and into the pancreatic mass or cyst. Masses in the pancreatic head use a transduodenal approach and those in the pancreatic body and tail use a transgastric approach. The biopsy channel is oriented so that the biopsy needle is advanced into the imaging plane allowing for real-time imaging of the biopsy. Once in the lesion, the stylet is removed, suction is applied using a syringe, and the needle is moved back and forth within the lesion to dislodge cells and pull them into the needle. If cystic, the cyst fluid is drained as much as possible. Depending on volume, cyst fluid can be submitted for routine cytology, biochemical and molecular analysis (see Pancreatic cysts, p. 350). Any visible mural nodule or solid component should be separately sampled. Obtaining formalin fixed paraffin embedded tissue from needle rinses or CB provides not only additional morphological information about the lesion, but readily available tissue for ancillary studies.²¹

Fig. 10.1 The FNA needle is guided by the echoendoscope. Aspirates of masses in the pancreatic head are performed through the duodenum, and those in the body and tail of the gland via the stomach.

In addition to CT and EUS-guided FNA, there are several other techniques that can provide tissue for interpretation. These techniques are no longer the procedures of choice, although they can be of value in selected clinical situations. For example, intraoperative FNA is a highly effective method of establishing a diagnosis of pancreatic malignancy.²² It, however, requires a surgeon to perform a laparotomy. Endoscopic retrograde cholangiopancreatography (ERCP) allows for sampling of the pancreatic juice. Although cytological examination of pancreatic juice can provide a tissue diagnosis, this is seldom the procedure of choice in the post-EUS era.²³ EUS-guided pancreatic duct aspiration is safe and can provide diagnostic material in a patient with pancreatic duct dilation.²⁴ Brushing cytology of the pancreatic duct has been reported to show high specificity for carcinoma, however, the sensitivity is lower than EUS-guided FNA.²⁵

Rapid on-site cytopathology interpretation has been shown to improve the diagnostic yield of EUS-guided FNA.^22,26,27 Interpretation of selected smears is routinely performed at our institution by a cytopathologist for all solid lesions that provide a sample from which adequate smears can be made. On-site assessment allows for appropriate triage of the specimen for ancillary studies, most importantly flow cytometry analysis of unfixed tissue and rarely for electron microscopy.²² Cyst fluids can produce direct smears if the fluid is thick, but thin watery or bloody fluids are sent to the laboratory fresh and undiluted, from which cytospins are made for routine stains and special stains for mucin (see Pancreatic cysts, p. 350). Triage of cyst fluid for biochemical analysis or molecular analysis can be performed either by the gastroenterologist or the pathology laboratory.

The overall risk of complications from EUS-FNA is relatively low at approximately 2%, with no severe or fatal incidents reported, and the risk appears only slightly higher than that for standard EUS alone.^28,29 The most common complications arising from FNA of the pancreas are haemorrhage and pancreatitis.^29–31 With percutaneous FNA, tumour seeding along the cutaneous needle track is an extremely rare event. Transperitoneal rather than needle track spread may be of greater concern.³² Subsequent to the work of Warshaw et al.,³² prospective studies of peritoneal washings, an indicator of transperitoneal seeding, in patients undergoing pancreatic surgery with or without prior FNA have concluded that CT-guided FNA does not appear to increase the risk for positive peritoneal washings.³³

EUS guided FNA of the pancreas is a technically difficult procedure and yields aspirates that are diagnostically challenging. Thus, the sensitivity of this procedure is variable, averaging 80% but ranging from 60% to 100%.^34–49 Sensitivity of the procedure can increase over time, reflecting increasing experience with this technique.⁵⁰ The specificity of diagnosis in the setting of a solid pancreatic mass is greater than 90%. The adequacy and sensitivity rates are generally higher when rapid onsite assessment is performed.⁵¹

It is difficult to compare the sensitivity of FNA among studies because of the wide variability in factors such as needle size, operator experience and improvement in radiological equipment. Additionally, the atypical and suspicious categories have been variably interpreted as negative or positive for the purposes of statistical analysis. The inaccuracies of pancreatic FNA appear to be almost entirely due to false negative reports. The sensitivity for cystic neoplasms is lower than that for solid neoplasms primarily due to the low cellularity of most of these cystic lesions.⁵²

Brush cytology has close to 100% specificity; it has about a 50% sensitivity rate due to false negative sampling and interpretation.²⁵ Definitive malignant interpretations are hindered by preparation artifact leading to indeterminate interpretations, as well as strict criteria and a high threshold for malignancy given the well-known atypia that generally occurs in inflamed, often stented ducts.^53,54

FNA samples from normal pancreas are of moderate cellularity and are composed mainly of acinar cells arranged in tight grape-like clusters or balls often attached to tissue fragments with ill-defined fibrovascular stroma (Fig. 10.2A), but also as individual acinar units, single cells and bare nuclei. Appreciation of this typical, organised, low-power architecture is important for distinguishing benign from malignant acinar proliferations, as well as acinar from endocrine proliferations. Cellular aspirates in which acinar cells present a solid cellular smear pattern of monomorphic cells can be mistaken for a neoplasm (Fig. 10.2B). Acinar cells are polygonal cells with ample cytoplasm which is dense and blue green with the standard Papanicolaou stain and purple and more obviously granular with a Wright–Giemsa stain (Fig. 10.2C). Nuclei are round with finely stippled chromatin. Small and eccentric nucleoli are often easily identified. The presence of these nucleoli helps in the identification of stripped acinar cells as epithelial and not lymphoid in nature.

Fig. 10.2 Pancreatic acinar cells. (A) Cohesive grape-like clusters of benign acinar cells are attached to a fibrovascular stroma and dispersed in the background (PAP). (B) When dispersed in small clusters and numerous single cells, cellular aspirates of benign acinar cells can be mistaken for a solid cellular neoplasm such as a pancreatic endocrine neoplasm (PAP). (C) Acinar cells are recognised by the typical acinar arrangement of polygonal cells with eccentric small round uniform nuclei, small nucleoli and abundant granular cytoplasm (Wright–Giemsa stain).

Ductal cells tend to be sparse in FNA smears from normal pancreas, but are more noticeable in the presence of duct obstruction secondary to tumour or chronic pancreatitis. They are readily identified in pancreatic duct brushings. These cuboidal to columnar cells are larger than acinar cells and are often arranged as monolayer sheets or strips of cells with a luminal edge of non-mucinous cytoplasm. Viewed en face the sheets have a honeycomb appearance with a uniform, geometric distribution of round, regular nuclei without crowding and well-defined cell borders (Fig. 10.3). The nuclei display evenly distributed finely granular chromatin and inconspicuous nucleoli that may become enlarged and prominent when reactive. The cytoplasm varies in amount from scanty to moderate and is dense and non-mucinous to the eye.

Fig. 10.3 Pancreatic ductal cells. Ductal cells most often appear as flat monolayered sheets of non-mucinous glandular cells with evenly distributed round uniform nuclei (PAP).

Islet cells are not usually recognised on FNA with routine stains, requiring special stains to highlight the neurosecretory granules for identification.

The principal contaminant of percutaneous FNA is mesothelium. Mesothelial cells may contaminate the FNA specimen when the lesion is approached anteriorly as peritoneum envelopes the anterior aspect of the pancreas. Mesothelial cells resemble benign ductal cells presenting in FNA smears with a similar flat, monolayered sheet-like arrangement. They are distinguished by their characteristic intercellular spaces or ‘windows’ (Fig. 10.4). Mesothelial cells can create a diagnostic pitfall especially when reactive and atypical leading to a false positive interpretation of carcinoma.

Fig. 10.4 Mesothelial cells. Percutaneous FNA with an anterior approach may retrieve mesothelial cells as a contaminant that resembles ductal cells. Mesothelial cells are recognised by the presence of intercellular spaces or ‘windows’ (Wright–Giemsa).

EUS-FNAs are invariably contaminated by epithelium and mucus from the gastrointestinal (GI) tract. Being able to recognise duodenal and gastric epithelium is essential for accurate interpretation of these specimens.^55,56 GI contamination from the duodenum and the stomach typically presents as flat monolayer sheets with a honeycomb pattern. Duodenal epithelium usually presents in large sheets studded with goblet cells, which have the appearance of a fried egg on alcohol-fixed preparations where the round central nucleus is surrounded by a clear halo (Fig. 10.5A). Gastric epithelium is more often present in small groups of glandular epithelium in which surface foveolar cells display mucinous cytoplasm that makes distinction from low-grade mucinous cyst lining epithelium virtually impossible (see below). One clue that may help is to appreciate the location of the cytoplasmic mucin, which tends to be limited to the upper third of the cytoplasmic compartment in gastric epithelium as opposed to more unevenly distributed mucin often filling the cytoplasmic compartment of cyst lining epithelium (Fig. 10.5B).

Fig. 10.5 (A) Duodenal epithelium. Flat monolayered sheets of non-mucinous epithelium studded with goblet cells distinguish duodenal epithelium from pancreatic ductal cells or cyst lining epithelium (PAP). (B) Gastric epithelium. Gastric foveolar cells may appear mucinous and often demonstrate mucin in the upper third of the cytoplasmic compartment forming an apical cup of mucin (PAP). (C) Duodenal epithelium. Duodenal villi may be misinterpreted as carcinoma or papillae of IPMN. Appreciation of goblet cells and intraepithelial lymphocytes will help identify the cells as duodenal in origin (PAP).

GI contamination can lead to under or over-interpretation of pancreatic FNAs. Mistaking benign GI groups as benign ductal cells can lead to interpreting an inadequate sample as adequate, contributing to a false negative interpretation. Conversely, reactive atypical GI groups can be mistaken for well-differentiated adenocarcinoma leading to a false positive interpretation. Both contaminating epithelia may appear complex and atypical from folding and discohesion or, in the case of duodenum, presenting as intact villi creating a diagnostic pitfall for over-interpretation as carcinoma (Fig. 10.5C). These groups of cells are generally distinguishable from ductal adenocarcinomas as they lack the characteristic nuclear features of malignancy, and contain goblet cells and lymphocytes within the epithelium.

Acute pancreatitis is a disease of sudden onset, which may follow episodes of alcohol abuse, trauma or obstruction of the pancreatic duct by stones or tumour. Release of destructive digestive enzymes causes extensive necrosis and inflammation of the parenchyma and surrounding tissue. Acute pancreatitis commonly involves the parenchyma diffusely and is a relative contraindication for FNA as there is a slight risk of exacerbation of the pancreatitis. However, the sequelae of acute pancreatitis, such as pseudocyst and abscess formation, and the hard nodular gland of chronic pancreatitis, may simulate cancer. Active chronic pancreatitis with a focal mass lesion is more likely to have an FNA performed to rule out tumour. Attention to the prominent inflammatory component on the slide admixed with benign pancreatic tissue should prevent potential pitfalls in diagnosis (Fig. 10.6).

Fig. 10.6 Acute pancreatitis. Inflammatory debris, fat necrosis and benign pancreatic tissue support this interpretation. Note the single group of acinar cells (upper right) (PAP).

Chronic pancreatitis is the result of repeated bouts of acute pancreatitis that lead to destruction of the acinar component and irreversible scarring of the parenchyma. A relative prominence of the endocrine component is seen on histology due to destruction of the acinar component, collapse of the remaining parenchyma and subsequent islet cell aggregation. The most common cause is alcohol abuse, but chronic pancreatitis is also commonly caused by chronic duct obstruction (e.g. from stones, thick secretions in cystic fibrosis, pancreatic divisum).³ The most important disease to be distinguished from chronic pancreatitis is pancreatic adenocarcinoma, which it can mimic clinically, on imaging, intraoperatively and on FNA. Aspiration of normal or injured acinar tissue may simulate a pancreatic endocrine neoplasm by yielding a solid cellular smear pattern (see Fig. 10.2B). Such a pattern may also be noted from FNA of a focus of islet cell aggregation. Replacement fibrosis may also hinder adequate sampling with a fine needle. When the FNA smear shows a predominantly inflammatory background with fibrosis and mixed acinar and ductal cells or only scant benign appearing ductal epithelium, the diagnosis is relatively straightforward (Fig. 10.7(A). However, a largely pure population of ductal cells with even mild atypia as defined by slight nuclear irregularity, uneven spacing and nucleoli (Fig. 10.7B) raises the possibility of well-differentiated adenocarcinoma. Prominent epithelial regeneration and reactive atypia of ducts and acini may cause difficulty in excluding carcinoma, and many of these cases are interpreted as indeterminate (atypical or suspicious) for malignancy.^57,58 Such atypia can be quite marked (Fig. 10.7C).

Fig. 10.7 Chronic pancreatitis. (A) Mixed acinar and ductal cells with few inflammatory cells and histocytes in the background (PAP). (B) Ductal cells with reactive atypia illustrated by slightly irregular nuclei, uneven spacing and nucleoli (PAP). (C) Glandular cells with marked atypia in chronic pancreatitis is a pitfall for false positive diagnosis (PAP).

AIP is a sclerosing inflammatory, pancreatocentric autoimmune disease of the pancreas that frequently presents as a mass forming lesion.⁵⁹ The majority of individuals present with obstructive jaundice, and thus this lesion frequently mimics pancreatic adenocarcinoma both clinically and radiologically. A tissue diagnosis of autoimmune pancreatitis is essential as this is a steroid responsive disease, and pancreatectomy is rarely justified. Histology is characterised by a periductal collar of lymphoplasmacytic inflammation, diffuse interlobular and/or lobular chronic inflammation, dense fibrosis and obliterative phlebitis (lymphoplasmacytic sclerosing pancreatitis).^59,60 Cell block preparations of small tissue fragments obtained at FNA or core biopsy are important for the recognition of these features (Fig. 10.8A). The cytological features sufficient to diagnose the condition on FNA are present in less than one-third of cases, and thus an FNA only occasionally provides a diagnosis of AIP.⁵⁷ The key cytological feature that should alert the pathologist to this diagnosis is the presence of cellular stromal fragments, the cellularity being due predominantly to embedded lymphocytes and plasma cells (Fig. 10.8B). Ductal cells with atypia in this setting should be interpreted with caution as such ductal atypia aspirated from the pancreas of an individual with AIP presenting with obstructive jaundice and a pancreatic ‘mass’ could be misdiagnosed as adenocarcinoma. Additionally, injured acinar epithelial cells may produce a solid cellular smear pattern resembling the parenchyma rich-stroma poor tumours of the pancreas such as pancreatic endocrine neoplasm. Serum IgG4 levels are usually elevated in AIP. A review of the imaging by an experienced radiologist and correlation with serum IgG4 levels should help avoid this pitfall. Additionally, FNA from AIP show none of the cardinal features of a well-differentiated ductal adenocarcinoma, namely nuclear anisonucleosis and nuclear membrane irregularities.

Fig. 10.8 Autoimmune pancreatitis. (A) Core biopsy or tissue fragments in cell block are very helpful in recognising the cellular stroma with embedded lymphocytes and plasma cells characteristic of this disease (H&E). (B) A clue to the diagnosis on FNA smears is recognising the characteristic cellular stroma with embedded lymphocytes and plasma cells (PAP).

(From Hruban RH, Pitman MB, Klimstra DS. Tumors of the Pancreas. Atlas of Tumor Pathology, 4th series, Fascicle 6. Washington, DC: American Registry of Pathology; Armed Forces Institutes of Pathology; 2007.)

Abscess formation may result from infected necrotic pancreatic tissue or superinfection of a pseudocyst secondary to acute pancreatitis. A CT scan cannot distinguish sterile inflammation from an infectious process. FNA of the fluid collection under aseptic conditions has become the procedure of choice for verification of bacterial infection.⁶¹ Immediate cytological examination may support the clinical diagnosis of an abscess if the smears consist of a marked acute inflammatory exudate and necrotic cellular debris. Drainage of a pancreatic abscess is a surgical emergency. Identification of bacteria with a rapid Gram stain is sufficient evidence for prompt surgical intervention and drainage.

Isolated forms of tuberculosis may rarely mimic a pancreatic malignancy.⁶² Such a diagnosis is prompted by the recognition of necrotising granulomas and confirmed with the identification of acid fast organisms, either on smears with an acid fast stain or by culture.

Adenocarcinoma arising from the exocrine pancreas constitutes ∼90% of all pancreatic malignancies, with more than 60% located in the head region. They are highly aggressive tumours occurring mainly in the fifth to seventh decades of life. Radiologically most adenocarcinomas appear as poorly defined, hypodense (CT) or hypoechoic (EUS) masses that distort the normal lobular architecture of the pancreas.⁶⁴ When located in the pancreatic head, they may be associated with pancreatic and bile duct stricture and downstream dual dilatation of both ducts (‘double-duct’ sign).⁶⁴ Rarely, a de-novo adenocarcinoma may appear cystic.

High-grade ductal adenocarcinoma

The majority of high-grade adenocarcinomas – that is, moderately and poorly differentiated adenocarcinomas – are easily diagnosed as malignant due to the characteristic high-grade features of carcinoma: crowded groups, cells with high nuclear to cytoplasmic ratio, irregular nuclear membranes, coarse irregular chromatin, single malignant cells, mitotic activity and background necrosis (Fig. 10.9). Rarely poorly differentiated adenocarcinomas may present with a prominent dispersed cell population that mimics acinar cell carcinoma, neuroendocrine tumour and lymphoma. Immunohistochemical stains such as cytokeratin and chromogranin as well as flow cytometry may be necessary to differentiate carcinoma from these tumours.

Fig. 10.9 High-grade adenocarcinoma. Epithelial cells with overtly malignant features including cellular clusters, large cells with high nuclear to cytoplasmic ratio, large irregular nuclei, single malignant cells and necrosis (Wright–Giemsa).

Well-differentiated ductal adenocarcinoma

Well-differentiated adenocarcinomas are more problematic as these lesions often show a deceptively bland appearance. The under diagnosis of well-differentiated adenocarcinoma as reactive epithelial changes is probably the greatest contributing factor for the relative low sensitivity of FNA. Several studies performed over the last two decades have addressed this issue.^65–67 Robins et al.⁶⁵ confirmed the diagnostic criteria for pancreatic adenocarcinoma, described by Mitchell and Carney:⁶⁸ three major criteria (nuclear crowding and overlap, irregular chromatin distribution and nuclear contour irregularity) and four minor criteria (nuclear enlargement, single malignant cells, necrosis and mitosis) to assist in making a diagnosis of adenocarcinoma. The presence of two or more major criteria or one major and three minor criteria were diagnostic of malignancy. Lin and Staerkel⁶⁶ identified four criteria that were consistently present in well-differentiated adenocarcinoma: (1) nuclear volume variation in cells within the same group, (2) nuclear membrane abnormalities, (3) nuclear crowding/overlap/three-dimensional fragments and (4) nuclear enlargement (>1.5 × RBC). On low magnification, sheets of tumour may initially resemble gastrointestinal contaminating epithelium. However, at the same low magnification, recognition of the uneven distribution of cells in the sheet or ‘drunken honeycomb’ appearance (Fig. 10.10), in contrast to the nuclei within the monolayers of gastrointestinal contaminating epithelium or benign pancreatic ductal epithelium that are evenly and geometrically spaced with the sheet (Fig. 10.11). well-differentiated adenocarcinoma may also demonstrate crowded, overlapped, irregularly shaped nuclei with anisonucleosis of 4:1 in a single sheet of cells (Fig. 10.12). The cells of reactive ductal epithelium, however, generally lack the other nuclear features of carcinoma such a variable enlargement in one sheet, parachromatin clearing and irregular nuclear membranes required for the diagnosis of adenocarcinoma (see Fig. 10.7B). Additionally, FNA smears from chronic pancreatitis tend to be less cellular, are associated with an inflammatory component, and show admixed acinar cells. Thus, aspirates with a significant number of non-ductal cells should be viewed with caution.

Fig. 10.10 Well-differentiated adenocarcinoma. Cohesive sheet of irregularly spaced nuclei in a ‘drunken honeycomb’ pattern (Wright–Giemsa).

Fig. 10.11 Benign glandular epithelium. GI contamination and benign ductal cells appear as flat monolayered sheets of evenly spaced non-mucinous epithelium in contrast to the ‘drunken honeycomb’ pattern of adenocarcinoma illustrated in 10.10 (Wright–Giemsa).

Fig. 10.12 Well-differentiated adenocarcinoma. Nuclear crowding and overlap, anisonucleosis of 4:1 in the same group and irregular nuclear membranes supports a malignant interpretation (PAP).

GI contamination can result in cellular smears, also producing a diagnostic challenge. Reactive changes in GI epithelium may result in slight nuclear irregularity, nuclear grooves and nuclear enlargement (>2 × RBC) (Fig. 10.13). The two most reliable features of a well-differentiated adenocarcinoma have been shown to be nuclear membrane irregularities and anisonucleosis, as defined by at least a 4:1 variation in nuclear size within a tissue fragment.⁶⁷

Fig. 10.13 Gastric epithelium. Uneven spacing can be seen due to normal gastric mucosal architecture. Note the islands of cells denoting gastric crypts (PAP).

A foamy gland pattern of adenocarcinoma is an exceptionally deceptively bland pattern of pancreatic adenocarcinoma characterised by abundant microvesicular (‘foamy’) cytoplasm (Fig. 10.14A).^69,70 The clue to recognising these cells as abnormal initially rests with the cytoplasm which is abundant and mucinous to the eye, an abnormal finding as normal pancreatic ductal epithelium is non-mucinous to the eye (see Fig. 10.2C). Subsequent close attention to the nuclear features should show sufficient irregularities to support a malignant interpretation (Fig. 10.14B).

Fig. 10.14 Foamy gland pattern of adenocarcinoma. (A) These deceptively malignant glandular cells demonstrate bland round nuclei but abnormally voluminous and visibly mucinous (foamy) cytoplasm (Wright–Giemsa). (B) Despite the low nuclear to cytoplasmic ratio, nuclear abnormalities are apparent as is abundant microvesicular mucinous cytoplasm on this cell block preparation (H&E).

Cytological findings: ductal adenocarcinoma

High-grade ductal adenocarcinoma

• Three-dimensional groups with nuclear crowding and overlap

• Easily identified intact malignant single cells

• Obvious nuclear membrane irregularities, hyperchromasia and coarse chromatin

• Mitosis and necrosis.

Well-differentiated ductal adenocarcinoma

• Nuclear contour irregularities

• Nuclear variation (>4:1) within a single group of cells

• Chromatin clearing and/or clumping

• ‘Washed-out’ nuclear chromatin (parachromatin clearing)

• Monolayer sheets with nuclear overlapping

• ‘Drunken honeycomb’ appearance

• Mitosis, necrosis and discohesion with single cells are useful but rarely present.

Surgery remains the mainstay of treatment of pancreatic ductal adenocarcinomas and remains the only therapy that offers long-term survival.⁷¹ Unfortunately, a significant number of patients are inoperable, and the radiation and/or chemotherapy that is offered to these individuals is rarely curative. The encouraging improvement in survival of patients undergoing neoadjuvant therapy has spurred a renewed interest in preoperative chemoradiation protocols.⁷²

Diagnostic pitfalls: ductal adenocarcinoma

• GI contaminating epithelium

• Reactive ductal groups in chronic pancreatitis

• Autoimmune pancreatitis.

Ancillary studies: ductal adenocarcinoma

Because of advances in our understanding of the molecular underpinnings of pancreatic carcinoma, numerous genes and proteins have been examined as diagnostic markers for pancreatic carcinoma. Currently, however, these tests have not been integrated into routine clinical practice.

• Oncogenes. K-ras mutations are detected in more than 90% of pancreatic adenocarcinomas, and thus could serve as a sensitive marker of pancreatic ductal adenocarcinoma.⁷³ Unfortunately, K-ras mutations are also detected in pre-neoplastic diseases of the pancreas, such as pancreatic intraepithelial neoplasia (PanIN) and chronic pancreatitis

• Tumour suppressor genes frequently inactivated in pancreatic cancer include p53, SMAD4 and p16. Loss of p53 and SMAD4, as documented by immunohistochemistry, can supplement traditional cytological diagnosis of pancreatic FNA.^74,75 In addition, loss of nuclear expression of SMAD4 can distinguish pancreatic adenocarcinomas from other adenocarcinomas, as SMAD4, while lost in >80% of pancreatic ductal adenocarcinomas, is only infrequently lost in adenocarcinomas of the ovary, colon, endometrium and lung⁷⁶

• Mucin markers: While normal pancreatic ductal epithelium generally lacks expression of apomucins, pancreatic ductal adenocarcinomas frequently overexpress these mucins, particularly MUC1 and MUC4.⁷⁷ In one study, the combination of MUC1 + /MUC2 − /MUC5AC+ was identified in 70% of pancreatic ductal adenocarcinomas, and was not observed in reactive samples⁷⁸

• Global expression profiling studies have lead to the identification of a number of biomarkers. Among these, mesothelin, S100P and prostate stem cell antigen show promise; these protein are either absent or under-expressed in non-neoplastic pancreas, while over-expressed in pancreatic adenocarcinomas.^79–81

While numerous morphological variants have been recognised, the identification of these variants, albeit immensely gratifying to the cytopathologist, are seldom of clinical relevance with few exceptions. Clinically these variants behave at least as aggressively as, if not more so, than conventional tubular ductal adenocarcinoma, and surgery remains the mainstay of treatment.

Undifferentiated carcinoma (pleomorphic carcinoma, pleomorphic giant cell carcinoma)

Undifferentiated carcinoma is a large and aggressive malignant neoplasm, that although may appear to show little evidence of epithelial differentiation, is both genetically and biologically a variant of pancreatic adenocarcinoma.³ The tumour is composed of large, pleomorphic cells, giant cells with malignant nuclei and/or ovoid to spindle shaped cells that form poorly cohesive groups supported by scant fibrous stroma (Fig. 10.15).⁸² The undifferentiated nature of the tumour raises a wide differential diagnosis, and while the majority of these lesions stain for cytokeratin, this reactivity may be focal and may not be identified on the FNA or in scant cell block preparations. Immunohistochemical stains for cytokeratin may be required to confirm the epithelial nature of the specimen and differentiate this neoplasm from metastatic melanoma (S100 and HMB-45 positive), haemopoietic (leucocyte common antigen positive among other more specific markers), mesenchymal (vimentin and other more specific markers such as desmin for smooth muscle and CD31 for vascular tumours), and germ cell tumours (alpha-fetoprotein, beta-HCG, placental alkaline phosphatase, among others).

Fig. 10.15 Undifferentiated carcinoma. (A) This variant of adenocarcinoma is composed of large bizarre discohesive epithelioid to spindled giant malignant cells. A rare osteoclast-type giant cell may be noted (PAP). (B) The large bizarre malignant cells may be few and widely scattered (Wright–Giemsa).

Cytological findings: undifferentiated carcinoma

• Marked cellularity with prominent tumour diathesis

• Predominantly isolated and poorly cohesive cells with few cell clusters

• Bizarre pleomorphic single cells

• Scattered multinucleated giant cells with malignant nuclei

• Osteoclast-type giant cells are few

• Spindled cells

• Bizarre mitotic figures.

Undifferentiated carcinoma with osteoclast-like giant cells

Undifferentiated carcinoma with osteoclast-like giant cells (UCOGC) is the currently accepted nomenclature that reflects the understanding that these tumours are fundamentally malignant epithelial neoplasms associated with benign appearing multinucleated giant cells that resemble the giant cells of a giant cell tumour of the bone.³ The presence of K-ras point mutations, and the association of many of these neoplasms with either conventional ductal adenocarcinoma or mucinous cystic neoplasms, is indicative of their epithelial differentiation.^3,83 On histology and cytology, the tumour is composed of osteoclast-like giant cells and atypical to overtly malignant polygonal to spindle-shaped epithelioid mononuclear cells (Fig. 10.16).⁸⁴ The malignant mononuclear cells are positive for cytokeratin, while the osteoclast-like giant cells are not. However, the cytokeratin reactivity is variable and some tumour cells may demonstrate either limited reactivity or complete lack of keratin expression. Thus, the absence of cytokeratin expression does not exclude this diagnosis.

Fig. 10.16 Undifferentiated carcinoma with osteoclast-like giant cells. Malignant mononuclear cells are associated with usually readily apparent osteoclast-type giant cells (PAP).

Cytological findings: undifferentiated carcinoma with osteoclast-like giant cells (UCOGC)

• Dual cell population

• Spindle to polygonal epithelioid atypical mononuclear cells

• Bland multinucleated osteoclast-like giant cells

• Osteoid may be present.

Benign and malignant processes in which multinucleated giant cells are a prominent feature should be distinguished from this tumour. The primary differential diagnosis is with undifferentiated (pleomorphic) carcinoma of the pancreas. Although undifferentiated carcinoma of the pancreas may show overlapping features with UCOGCs, undifferentiated carcinomas contain giant cells predominantly with malignant nuclei and only rare benign appearing osteoclast-like giant cells in contrast to the benign appearing osteoclast-like giant cells predominating in UCOGC tumours. Other malignant tumours that may yield bizarre multinucleated malignant cells include metastatic anaplastic carcinoma of the thyroid, malignant melanoma, hepatocellular carcinoma, high-grade sarcomas and trophoblastic tumours. Tuberculosis, fat necrosis, pseudocysts, fungal infections and foreign body giant cell reactions are among the benign lesions in which multinucleated giant cells may be seen.⁸² However, these benign entities are extremely rare in the pancreas and are not associated with the usually overtly malignant stromal mononuclear cells of UCOGC.

Diagnostic pitfalls: undifferentiated carcinoma with osteoclast-like giant cells

• Undifferentiated (pleomorphic) carcinoma of the pancreas

• Other high-grade primary and metastatic malignant neoplasms with tumour giant cells

• Benign conditions with reactive stroma and giant cells.

Adenosquamous carcinoma

This rare neoplasm is characterised by the presence of a variable proportion of mucin-producing glandular and squamous epithelial cells.^85,86 The squamous component should accounts for at least 30% of the tumour.⁶³ A few reports have described the FNA findings of adenosquamous carcinoma.^86,87 As in histology, the proportions of squamous and glandular cells vary. The squamous element may dominate or may be the only cell type seen, and single cells with cytoplasmic mucin vacuoles may be the only evidence of glandular differentiation (Fig. 10.17). Pure squamous cell carcinomas of the pancreas are virtually non-existent. Hence, if glandular differentiation cannot be identified, a metastatic squamous cell carcinoma should be considered in the differential diagnosis.

Fig. 10.17 Adenosquamous carcinoma. Cluster of malignant squamous cells and neoplastic mucin-containing glandular cells (PAP).

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Like this:

Like Loading...

Related

Related posts:

1. New techniques
2. Other lymphoreticular organs
3. Thyroid gland
4. Lymph nodes

Stay updated, free articles. Join our Telegram channel

Join