High Grade Neuroendocrine Carcinoma (Small Cell Carcinoma) of the Breast
Differential Diagnosis
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Neuroendocrine Carcinomas: Low Grade, High Grade or NOS
- Low grade neuroendocrine carcinoma by definition has low grade cytologic features
- Round, regular to mildly irregular nuclei up to 2-3x the size of a RBC
- No comedo necrosis
- Neuroendocrine carcinoma NOS
- Lacks the specific features of the other two
- High grade neuroendocrine carcinoma
- Most demonstrate features of small cell carcinoma
- Very rare carcinomas have been reported that demonstrate features similar to pulmonary large cell neuroendocrine carcinomas
- Low grade neuroendocrine carcinoma by definition has low grade cytologic features
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Primary vs. metastatic small cell carcinoma
- Metastasis must be excluded whenever small cell carcinoma is found in the breast
- ER positive supports a primary carcinoma
- Small cell carcinomas of other sites are reported as negative
- Negative result is non-contributory
- TTF1 negative supports a breast primary
- 90% of lung small cell carcinomas are positive
- Positive result is non-contributory
- Clinical and imaging search for another primary site may be useful