Although the criteria for objective diagnosis are not universally agreed upon, most authors have defined apocrine carcinoma as a uniform population of cells with abundant granular, eosinophilic cytoplasm; distinct cell borders; and usually, but not always, high-grade nuclear features, with prominent nucleoli.1–3 Based on this definition, apocrine carcinoma is a rare entity, in most series accounting for less than 1% of all cases.4, 5
We used a restrictive definition of apocrine ductal carcinoma in situ (DCIS). None of the cases reported in our recent study6 met that definition. We do not consider the presence of apocrine snouts alone, as sometimes is seen in other forms of DCIS, to be sufficient for a diagnosis of apocrine carcinoma. Nucleolar prominence alone is insufficient as well, because it also can be observed in apocrine metaplasias.