Invasive micropapillary carcinoma of the breast: a prognostic study.

Invasive micropapillary carcinoma (IMC) of the breast is a rare variant of infiltrating ductal carcinoma that has been associated with an extremely high incidence of lymph node metastases. Follow-up studies on patients with pure IMC breast cancer histology have been limited by low patient numbers, short duration of follow-up, and a lack of multivariate analyses. Using invasive breast cancers from 1,287 patients (median follow-up, 13.8 years), histological review showed 21 cases (1.7%) with pure IMC histology. Pure IMC histology was associated with high-grade histology (P = .04), metastases to regional lymph nodes (P < .001), a high mitotic index (P = .02), and erbB-2 immunopositivity (P = .007). Univariate analyses showed a strong association between IMC histology and shortened survival (disease-free survival [DFS], P = .0052; median, 44 months for IMC and 63 months for non-IMC; disease-specific survival [DSS], P = .014; medians, 71 and 78 for IMC and non-IMC, respectively) only in an analysis of all patients. Because only 1 case of node-negative IMC histology was available, univariate analysis of IMC histology was performed only on node-positive patients without significance. Multivariate analyses comparing IMC histology with either node-positive or all other breast cancers failed to show independent prognostic significance. In summary, breast cancer patients with pure IMC histology showed survival rates similar to those of other patients with equivalent numbers of lymph node metastases.