Neuroendocrine Carcinoma of the Breast, NOS

Definition

Breast carcinoma expressing predominant neuroendocrine differentiation but lacking specific cyto-architectural features of low grade or high grade neuroendocrine carcinoma

At least 50% of cells are neuroendocrine marker positive
- We require either synaptophysin or chromogranin
- We do not consider neuron specific enolase to be sufficiently specific for this diagnosis
Any conventional breast carcinoma pattern excluding those of:
- Low grade neuroendocrine carcinoma
  - Solid sheets, insular pattern or large round masses
  - Stippled chromatin
  - Low grade cytologic features
- High grade neuroendocrine carcinoma
  - Small cell carcinoma
Small numbers reported but there is no clear clinical difference from conventional carcinoma