Neuroendocrine/Small Cell Carcinoma
Key Facts
Terminology
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WHO classification recognizes 3 categories of NEBC
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Solid neuroendocrine carcinoma: Most common
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Large cell neuroendocrine carcinoma
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Small cell/oat cell carcinoma: Very rare
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Carcinomas must have typical histologic features and express at least 1 neuroendocrine marker in > 50% of cells to qualify
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However, this is a heterogeneous group of carcinomas and not all will easily fit into these 3 groups
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Etiology/Pathogenesis
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Gene expression profiling has shown that solid neuroendocrine carcinoma has transcriptional pattern identical to type B mucinous carcinomas (cellular mucinous carcinomas)
Clinical Issues
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2-5% of breast carcinomas
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Information on prognosis is limited due to small numbers of patients and varying definitions of NEBC
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Solid neuroendocrine carcinoma, especially if associated with solid papillary pattern or mucin production, has better prognosis
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Other types may have worse prognosis
Top Differential Diagnoses
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Primary carcinoid tumor of breast
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Metastatic carcinoid tumor
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Metastatic small cell carcinoma
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Breast carcinomas of no special type
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Alveolar lobular carcinoma
Histologic features of neuroendocrine differentiation include an organoid growth pattern with uniform epithelioid cells having moderate amounts of cytoplasm, dispersed chromatin, and rosette formation. |
Neuroendocrine breast carcinoma must express a neuroendocrine marker such as chromogranin in ≥ 50% of tumor cells  . Normal breast epithelial cells are negative for these markers  . |
TERMINOLOGY
Abbreviations
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Neuroendocrine breast carcinoma (NEBC)
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Solid neuroendocrine breast carcinoma (SNEBC)
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Small cell/oat cell breast carcinoma (SCOCBC)
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Large cell neuroendocrine breast carcinoma (LCNEBC)
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Synonyms
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Invasive carcinoma with endocrine differentiation (argyrophilic carcinoma)
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Mammary carcinoma with endocrine features
Definitions
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WHO classification recognizes 3 categories of neuroendocrine breast carcinoma
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Solid neuroendocrine breast carcinoma
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Small cell/oat cell breast carcinoma
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Large cell neuroendocrine breast carcinoma
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Carcinomas must have “morphologic features similar to those of neuroendocrine tumors of both gastrointestinal tract and lung”
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Tumors must express at least 1 neuroendocrine marker in > 50% of cells to qualify
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Some carcinomas with typical morphologic appearance will not express neuroendocrine markers
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Alternatively, not all carcinomas that express neuroendocrine markers have a distinctive morphologic appearance
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This is a heterogeneous group of carcinomas; not all cases will easily fit into 3 groups as defined by WHO
ETIOLOGY/PATHOGENESIS
Biology of NEBC
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Gene expression profiling analysis of NEBC
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NEBC belongs to luminal A subgroup
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SNEBC has transcriptional pattern identical to type B mucinous carcinoma (hypercellular type)
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This association is present whether or not mucinous carcinomas express neuroendocrine markers
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Type A mucinous carcinomas (paucicellular) cluster in separate but related group
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CLINICAL ISSUES
Epidemiology
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Incidence
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NEBCs comprise 2-5% of breast carcinomas
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Age
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NEBC has same age distribution as carcinomas of no special type; median age at diagnosis is 61 years
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Presentation
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NEBC usually presents as palpable mass or mammographic density
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Calcifications have not been associated with these tumors
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Very rare breast carcinomas produce ectopic hormones
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Human chorionic gonadotropin, calcitonin, adrenocorticotrophic hormone, parathormone, and epinephrine have been reported
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Clinical symptomatology from these hormones is very rare
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Treatment
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Not altered by presence of neuroendocrine markers
Prognosis
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Information is limited due to small numbers of patients and varying definitions of NEBC
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In small studies, SNEBC, especially if associated with solid papillary pattern or mucin production, has better prognosis
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In 1 study, LCNEBC had worse prognosis compared to matched controls with carcinomas of no special type
IMAGE FINDINGS
Radiographic Findings
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No specific imaging features
MACROSCOPIC FEATURES
General Features
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No specific gross features
MICROSCOPIC PATHOLOGY
Histologic Features
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Histologic types of NEBC are recognized in WHO classification
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Solid neuroendocrine breast carcinoma (SNEBC)
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Most common type of NEBC
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Tumors form circumscribed or lobulated masses that may be solitary or multiple
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Cell nests may be separated by delicate septae; some have solid papillary pattern
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Cell type can vary from spindled to epithelioid
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Peripheral palisading and rosette formation may be present
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About 25% are associated with at least focal extracellular mucin or intracellular mucin
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Small cell/oat cell breast carcinoma (SCOCBC)
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