Secretory carcinoma of the breast is rare, and is one of the few breast cancer types that is associated with a recurrent translocation; the t(12;15)(q13;q25) translocation which produces the ETV6-NTRK3 fusion product. (This rearrangement is also seen in mammary analogue secretory carcinoma of salivary gland, infantile fibrosarcoma, and congenital mesoblastic nephroma.) Secretory carcinoma can occur at any age but makes up a slightly increased proportion of breast carcinomas in girls and young women (< 20 years). Secretory carcinoma is one of the ‘triple negative’ breast cancers – it typically does not stain for ER, PR, or Her2 biomarkers (this case had heterogeneous ER positivity, not shown). In spite of this, this subtype has a relatively good prognosis and there are too few cases of secretory carcinoma to establish a clear benefit for adjuvant chemotherapy or radiotherapy.

The pathologic features include large infiltrative nests of cohesive cells, with both solid and microcystic, and a separate area of tubules with an invasive pattern. Part of the sampled lesion shows a sclerotic fibrous stroma. The cells have a moderate amount of granular eosinophilic (or occasionally pale and foamy) cytoplasm. Numerous luminal spaces filled with eosinophilic secretory material are seen. The nuclei are low grade and have little pleomorphism. Mitotic figures are scarce. It stains positively for S100 and EMA by immunohistochemistry, with luminal secretions highlighted by PAS or Alcian blue staining.