Management of Unusual Histological Types of Breast Cancer

Abstract

There is increased understanding of the heterogeneity of breast tumors, with greater emphasis now being placed on histological and molecular profiles and, in particular, their implications for prognosis and therapy. This review addresses breast cancers of unusual histological subtype with an approximate incidence ≤1%. Given the rarity of these tumors, the literature contains primarily case reports, small series, and population-based studies. Data are heterogeneous and almost entirely retrospective, frequently gathered over long time periods, in the context of changing pathological techniques and reporting. In addition, our understanding of the disease biology and therapeutic context has also evolved significantly over this time. There is often limited information about the specific therapies used and the rationale for choosing such an approach. Meaningful comparisons of treatment modalities are not feasible and it is not possible to define management guidelines. Instead, this review correlates the available information to give an impression of how each subgroup behaves—of the favored surgical technique, responses to therapy, and prognosis—as well as the emerging molecular data, highlighting new research areas for potential target in clinical trials. Each tumor subtype described represents a small but real cohort of patients with breast cancer, and although inferences may be made from this review, we are mindful of the paucity of data. The management of each patient must be considered in the context of their unique clinical presentation and correlated with the evidence-based principles that apply to more common breast cancer histologies.