Histological type and typing of breast carcinomas and the WHO classification changes over time

Abstract

The World Health Organization's new classification of breast tumors has just been published. This review aims to examine the morphological categorization of breast carcinomas which is still principally based on histological features and follows the traditions of histological typing. It gives a subjective and critical view on the WHO classifications and their changes over time, and describes the changes related to some of the most common or challenging breast carcinomas: in situ carcinomas, invasive breast carcinomas of no special type, lobular, cribriform, tubular, mucinous, papillary, metaplastic carcinomas and carcinomas with medullary pattern and those with apocrine differentiation are discussed in more details. Although the 5^th edition of the classification is not perfect, it has advantages which are mentioned along with problematic issues of classifications.

Keywords: WHO classification; breast carcinoma; histological type.

Figure 1.

LN with aberrant membranous E-cadherin complex protein expression. Fibroadenoma with lobular neoplasia, which can be seen between the 12 and the 3 o’clock position (A: HE x5); with a higher magnification, the discohesive cellular composition fulfils the diagnostic criteria of lobular neoplasia (B: HE x70), but the membranous staining with E-cadherin (C, x40), b-catenin (D, x40) and p120 (E, x40) are aberrant. S100 highlights the myoepithelial cells (F, x40).

Figure 2.

Tubules in ILC. This is an ILC with some trabecular pattern (alveolar elsewhere) which demonstrates some tubules (arrow and inset; b-catenin, x5 and x20 - inset). All tumor cells are b-catenin negative (and were also E-cadherin negative and – high molecular weight cytokeratin/34bE12 positive – not shown.) Whether these tubules are genuine ILC components or minor non-ILC component lacking the function of the E-cadherin-complex is subject to interpretation, but the former is favoured.

Figure 3.

Mixed IBC-NST and lobular carcinoma or ductulolobular carcinoma? The illustrated tumor was diagnosed on core needle biopsy as IBC-NST (A, HE, x40) and had a HER2-positive (+) (B, HER2, x400), ER-negative (-), PR- phenotype (not shown). After primary systemic treatment with a taxan containing regimen and trastuzumab. Following this neoadjuvant therapy the tumor bed was suggestive of pathological complete regression (C, HE x100), except for about a 10% area where ILC was identified (D, HE x400) with the typical E-cadherin- (not shown), b-catenin- (E, b-catenin x400), ER+ (F, ER x400), PR+, HER2- phenotype, proving a well defined mixed tumor of different histological types and biomarker expression.