'Pure' invasive apocrine carcinoma of the breast: a new clinicopathological entity?

Invasive apocrine carcinoma (IAC) of the breast has a similar prognosis to infiltrating ductal carcinoma not otherwise specified (IDC-NOS). The existence of a pure IAC subtype (PIAC) and its possible prognostic implications have not been fully investigated. To this end, pathological inclusion criteria for the diagnosis of PIAC were defined and three pathologists reviewed their slides blind to identify it. To assess its clinical behavior, a case-control evaluation was performed, for which 122 cases were selected. There was 100% agreement among the pathologists on the diagnosis: PIAC was identified in 37 cases and IDC-NOS, in 68, while 17 cases were categorized as complex IAC. The probability of 6-year survival was 0.72 for PIAC and 0.52 for IDC-NOS (P=0.02), and was still better after adjustment for tumor grade and axillary status. PIAC may be a distinct clinicopathological entity with a less aggressive behavior than high-grade IDC-NOS and might be regarded as an independent prognostic factor in early breast cancer.