Answer: In-situ and infiltrating apocrine ductal carcinoma

Histology: The lesion is composed entirely of apocrine cells; that is, cells with abundant granular pink cytoplasm, and nuclei with generally vesicular chromatin and prominent nucleoli. There is an infiltrating component characterized by desmoplasia and irregularly placed tumor cell nests. The presence of in situ carcinoma is confirmed by the presence of similar cells within ducts showing coarse chromatin, irregular nuclear membranes, irregularly-shaped prominent nucleoli and necrosis. Focal cribriform architecture is also identified.

Discussion: Lobular carcinoma may occasionally have apocrine features, but should not show the marked pleomorphism and gland formation seen in the current case. The irregular shape of the nests and presence of desmoplasia is diagnostic of invasion. The marked nuclear chromatin irregularities and presence of necrosis allow one to diagnose this lesion as apocrine DCIS, as opposed to an atypical apocrine proliferation. This distinction can otherwise be difficult, since benign apocrine lesions are typically monotonous and have uniform cytology with prominent nucleoli.

While many invasive breast cancers show apocrine features focally (particularly when evaluated by immunohistochemistry for GCDFP), pure apocrine carcinomas such as the current lesion are rare, comprising less than 4% of cases. These tumors are typically negative for estrogen and progesterone receptor (as the current case was) but strongly positive for the androgen receptor. There is no evidence that this histologic pattern is in and of itself associated with a better or worse prognosis once stage and grade are accounted for.

Reference(s):
Advances in Anatomic Pathology 2004; 11: 1-9.