Peritoneum/Omentum

6.1 NONINVASIVE IMPLANTS ASSOCIATED WITH SEROUS BORDERLINE TUMOR (Atypical Proliferative Serous Tumor [Typical Serous Borderline Tumor] or Noninvasive Low-Grade Serous Carcinoma [Micropapillary Serous Borderline Tumor]) VS. ENDOSALPINGIOSIS

	Noninvasive Implants	Endosalpingiosis
Age	50 years (median)	Premenopausal
Location	Peritoneal surfaces, including omentum	Peritoneal surfaces (including omentum) and/or lymph nodes
Symptoms	Symptoms attributable to ovarian mass	Asymptomatic
Signs	May appear as small nodules on peritoneal surfaces or be a microscopic finding	No gross lesion; microscopic finding
Etiology	Most implants are clonally related to the primary ovarian tumor; they are thought to become detached from the tumor and directly implant onto peritoneal surfaces as opposed to being of independent primary peritoneal origin	Unknown; may be due to exfoliated fallopian tube epithelium that implants onto peritoneal surfaces (analogous to mechanism for endometriosis); a coexisting ovarian serous borderline tumor and/or implants can be present
Histology	1. Variable number of foci present on serosal surfaces or within septa between lobules of adipose tissue in the omentum (Fig. 6.1.1)	1. Variable number of foci present on serosal surfaces or within septa between lobules of adipose tissue in the omentum
	2. Lesional foci composed of glands, papillae, and/or solid nests (Fig. 6.1.2)	2. Lesional foci composed of only glands (rare limited intraglandular papillary formations can be seen) (Fig. 6.1.7)
	3. Lesional foci may be isolated or crowded	3. Lesional foci usually isolated but occasionally can have some degree of crowding (Fig. 6.1.8)
	4. Lesional epithelium may display complexity with stratification and detached clusters; consists of bland tubal-type cells (Figs. 6.1.3 6.1.4, 6.1.5, 6.1.6)	4. No epithelial complexity; glands lined by single layer of bland tubal-type cells (Fig. 6.1.9)
	5. Implants can be purely epithelial-type or have desmoplastic stroma (the latter often present as a plaque on surface of serosa) (Fig. 6.1.1)	5. No desmoplasia
	6. Psammoma bodies can be present	6. Psammoma bodies can be present (Fig. 6.1.10)
Special studies	Of no use for this differential diagnosis	Of no use for this differential diagnosis
Treatment	Surgical excision, including debulking of all grossly visible disease	No therapy necessary
Prognosis	The presence of implants qualifies for advanced-stage serous borderline tumor (usually stage II or III); women with noninvasive implants have a significantly higher risk for subsequent development of low-grade serous carcinoma compared with women who have serous borderline tumors without implants	Benign; in the setting of an ovarian serous borderline tumor, endosalpingiosis does not result in upstaging or affect prognosis

Figure 6.1.1 Desmoplastic noninvasive implant of atypical proliferative (borderline) serous tumor with plaque-like involvement of surface of omentum.

Figure 6.1.2 Desmoplastic noninvasive implant of atypical proliferative (borderline) serous tumor. The glands at low-power magnification can resemble endosalpingiosis.

Figure 6.1.3 Desmoplastic noninvasive implant of atypical proliferative (borderline) serous tumor. The glands exhibit some degree of epithelial stratification.

Figure 6.1.4 Epithelial-type noninvasive implant of atypical proliferative (borderline) serous tumor with papillae.

Figure 6.1.5 Epithelial-type noninvasive implant of atypical proliferative (borderline) serous tumor with papillae (higher power magnification of Fig. 6.1.4). Note the presence of psammoma bodies.

Figure 6.1.6 Epithelial-type noninvasive implant of atypical proliferative (borderline) serous tumor with papillae and detached epithelial clusters.

Figure 6.1.7 Endosalpingiosis with simple and cystically dilated glands.

Figure 6.1.8 Endosalpingiosis with more crowding of glands than is typically seen.

Figure 6.1.9 Endosalpingiosis composed of a single layer of tubal-type epithelium, including ciliated cells.

Figure 6.1.10 Endosalpingiosis with numerous psammoma bodies.

6.2 NONINVASIVE IMPLANTS ASSOCIATED WITH SEROUS BORDERLINE TUMOR (Atypical Proliferative Serous Tumor [Typical Serous Borderline Tumor] or Noninvasive Low-Grade Serous Carcinoma [Micropapillary Serous Borderline Tumor]) vs. LOW-GRADE SEROUS CARCINOMA (Invasive Implants)

Figure 6.2.1 Epithelial-type noninvasive implant with complex papillary architecture.

Figure 6.2.2 Epithelial-type noninvasive implant showing papillae with fibrous cores.

Figure 6.2.3 Epithelial-type noninvasive implant with detached epithelial clusters in epithelial-lined spaces.

Figure 6.2.4 Desmoplastic noninvasive implant. Glands are embedded within desmoplastic stroma.

Figure 6.2.5 Desmoplastic noninvasive implant. Individual epithelioid cells with abundant eosinophilic cytoplasm are present within desmoplastic stroma.

Figure 6.2.6 Low-grade serous carcinoma (invasive implant) with infiltrating pattern.

Figure 6.2.7 Low-grade serous carcinoma (invasive implant) with infiltrating pattern. Note the haphazard arrangements of nests.

Figure 6.2.8 Low-grade serous carcinoma (invasive implant) with the same type of micropapillary pattern seen in an exophytic form of ovarian noninvasive low-grade serous carcinoma (micropapillary serous borderline tumor). The interface between epithelium and stroma is smooth without infiltration, but this pattern is considered an “invasive implant” per expanded criteria.

Figure 6.2.9 Low-grade serous carcinoma (invasive implant) with cribriform pattern.

Figure 6.2.10 Low-grade serous carcinoma (invasive implant). These solid/micropapillary nests are present within clear lacunar spaces.

6.3 NONDIAGNOSTIC LOW-GRADE SEROUS PROLIFERATION VS. LOW-GRADE SEROUS CARCINOMA

	Nondiagnostic Low-Grade Serous Proliferation	Low-Grade Serous Carcinoma
Age	Usually premenopausal	Most peri- or postmenopausal
Location	Intra-abdominal/pelvic serosal/peritoneal sites	Intra-abdominal/pelvic serosal/peritoneal sites; may have parenchymal involvement of intra-abdominal/pelvic organs or lymph nodes (Figs. 6.3.7 and 6.3.8)
Symptoms	May be incidental microscopic finding in specimens from surgeries performed for other indications, or patients may present with pelvic/abdominal pain	Abdominal pain, but may be incidental finding
Signs	May be incidental microscopic finding, or patients may have adhesions or peritoneal granules/nodules; however, a mass should not be present	Nodules, adhesions, and/or dominant mass
Etiology	“Low-grade serous proliferation” is a descriptive diagnosis for an ill-defined heterogeneous category that may represent either:	Precursor lesions include endosalpingiosis and serous borderline tumor with stepwise progression to carcinoma involving BRAF/KRAS mutations
	(A) secondary microscopic peritoneal involvement by a low-grade serous tumor (borderline tumor or carcinoma), in which the low-grade serous tumor is only identified after the initial surgery, and that the peritoneal low-grade serous proliferation is insufficient for further classification by itself, or (B) a microscopic peritoneal lesion in which a low-grade serous tumor is not identified after further clinical evaluation and that the low-grade serous proliferation is insufficient for further classification This nondiagnostic lesion may resemble noninvasive implants, but there is no known serous borderline tumor elsewhere; The lesion discussed herein is similar to what other authors have described as “peritoneal serous borderline tumor” and “peritoneal serous micropapillomatosis of low malignant potential”; however, this nondiagnostic low-grade serous proliferation is insufficient for further classification as a serous borderline tumor or low-grade carcinoma (including the “serous psammocarcinoma” variant) as it lacks the diagnostic histologic features of either of those tumors
Histology	1. Lesion involves serosal/peritoneal surfaces without invasion of underlying tissue (Figs. 6.3.1 and 6.3.2); expanded criteria for “invasive implants” (see Section 6.2) should also be absent	1. Lesion involves serosal/peritoneal surfaces, but invasion of underlying tissue (or expanded criteria for “invasive implants” [see Section 6.2]) should be present (Figs. 6.3.9 and 6.3.10)
	2. Lesion may be unifocal or multifocal	2. Lesion may be unifocal or multifocal, but many cases will have widespread disease
	3. Composed of mixture of glands, papillae, and/or solid nests; similar to noninvasive implants associated with serous borderline tumors (Figs. 6.3.3 and 6.3.4); degree of crowding of epithelial structures not as great as in carcinoma (Fig. 6.3.4); no haphazard arrangement; lesional epithelium may be embedded within adhesions and associated with psammoma bodies (Figs. 6.3.5 and 6.3.6)	3. Composed of mixture of glands, papillae, and/or solid nests with marked crowding of epithelial structures and haphazard arrangement; psammoma bodies may be present (Figs. 6.3.7 6.3.8, 6.3.9, 6.3.10)
	4. Lesional epithelium may have stratification and detached epithelial clusters (Fig. 6.3.2)	4. Lesional epithelium may have stratification and detached epithelial clusters
	5. Consists of bland tubal-type epithelium (Figs. 6.3.4 and 6.3.6)	5. Consists of bland tubal-type epithelium although ciliated cells are scant to absent; atypia may be present but is low-grade
	6. A background of endosalpingiosis may be present	6. A background of endosalpingiosis may be present
Special studies	Of no use for this differential diagnosis	Of no use for this differential diagnosis
Treatment	Further clinical evaluation is necessary to exclude the possibility that this represents either noninvasive implants of a serous borderline tumor or subtle metastases of a low-grade serous carcinoma elsewhere	Hysterectomy and bilateral salpingo-oophorectomy, including debulking of all grossly visible disease; further management options include observation or chemotherapy
Prognosis	Unknown; short-term follow-up based on relatively limited data for lesions with a histologic appearance similar to what has been reported in the literature as “peritoneal serous borderline tumor” and “peritoneal serous micropapillomatosis of low malignant potential” (but without a serous borderline tumor elsewhere) suggest a generally favorable outcome, typically without progressive disease; in the absence of a coexisting borderline tumor or carcinoma detected upon further clinical investigation, it is unclear whether this lesion may (a) represent a precursor to a low-grade serous tumor that might take years to fully manifest as such or (b) be associated with an increased risk for a subsequent low-grade serous tumor; accordingly, long-term follow-up is suggested.	Median survival, 48-82 months (advanced stage ovarian low-grade serous carcinoma)

Figure 6.3.1 Nondiagnostic low-grade serous proliferation distributed along the septa of lobules of adipose tissue within the omentum. No invasion into underlying tissue is present.

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