Immunohistochemically defined subtypes and outcome of apocrine breast cancer.

BACKGROUND: Conflicting data are available in the literature on the outcome of invasive apocrine carcinoma (IAC), possibly related to a heterogeneous classification of these tumors.

PATIENTS AND METHODS: A series of 6899 consecutive patients with invasive ductal carcinoma (IDC) not otherwise specified and 72 patients with immunohistochemically defined IAC who received surgery at the European Institute of Oncology between 1997 and 2005 were included. We then explored patterns of recurrence of IAC according to 2 immunohistochemically defined tumor subtypes: pure apocrine carcinoma (estrogen [ER] and progesterone [PgR] receptor negative, and AR positive) and apocrine-like carcinoma (ER or PgR positive and AR negative).

RESULTS: The diagnosis of pure apocrine carcinoma was correlated with a worse outcome in terms of DFS (hazard ratio [HR] 1.7; 95% confidence interval [CI], 1.01-2.86; P = .0010) if compared with IDC, whereas IDC and apocrine-like breast cancers showed a similar outcome in terms of DFS and overall survival. Patients with pure apocrine carcinoma had an increased risk in contralateral breast cancer (HR, 4.12; 95% CI, 1.22-14; P = .02).

CONCLUSION: Pure apocrine carcinoma represents a distinct subtype of breast cancer with a significantly worse DFS as compared with IDC. AR determination might have an important prognostic implication in IAC. Moreover, AR-targeted therapy should be further explored within these tumors.