An update on the pathological classification of breast cancer

Abstract

Breast cancer (BC) is a heterogeneous disease, encompassing a diverse spectrum of tumours with varying morphological, biological, and clinical phenotypes. Although tumours may show phenotypic overlap, they often display different biological behaviour and response to therapy. Advances in high-throughput molecular techniques and bioinformatics have contributed to improved understanding of BC biology and refinement of molecular taxonomy with the identification of specific molecular subclasses. Although the traditional pathological morphological classification of BC is of paramount importance and provides diagnostic and prognostic information, current interest focusses on the use of a single gene and multigene assays to stratify BC into distinct groups to guide decisions on systemic therapy. This review considers approaches to the classification of BC, including their limitations, and with particular emphasis on the fundamental role of morphology in establishing an accurate diagnosis of primary invasive carcinoma of breast origin. This forms the basis for further morphological characterization and for all other approaches to BC classification that are used to provide prognostic and therapeutic predictive information.

Keywords: breast cancer; classification; clinical; differentiation; grade; molecular; outcome; stage.

Figure 1

A case of mucinous cystadenocarcinoma featuring complex papillary growth pattern (A) and prominent cystic spaces (B) with mucinous differentiation (C) mimicking mucinous cystadenocarcinoma of the ovary and some other organs.

Figure 2

A case of tall cell carcinoma with reversed polarity featuring nuclei placed away from the basal border (A), nuclear groove and nuclear overlapping (B) similar to the tall cell variant of papillary thyroid carcinoma.