Histology of Luminal Breast Cancer

Abstract

Background: Invasive breast cancer (IBC) can be categorized into prognostic and predictive molecular subtypes (including luminal breast cancer) using gene expression profiling. Luminal IBC comprises a variety of histological subtypes with varying clinical and pathological features.

Summary: IBC of no special subtype is the most common histological subtype in general and likewise within luminal IBC. Classical invasive lobular breast cancer, typically clustering into luminal subgroup, is characterized by discohesive growth and loss of E-cadherin expression. Infrequent, morphologically distinct luminal IBC subtypes are tubular, invasive cribriform, mucinous, and invasive micropapillary carcinomas. Breast carcinoma with apocrine differentiation, with characteristic expression of androgen receptor (AR), often clusters into the luminal AR category. Rarely, neuroendocrine neoplasms of the breast can be seen. IBC of the male breast usually matches with the luminal subtype.

Key messages: Independently from histological subtypes, invasive breast cancer (IBC) can be divided into molecular subtypes based on mRNA gene expression levels. Using this molecular subtyping, risk scores based on gene expression profiling (established for hormone receptor-positive, HER2-negative IBC), grading, and Ki-67 index, prognosis of patients with luminal breast cancer and response to chemotherapy can be predicted. In routine diagnostics, the expression of estrogen receptor (ER) and progesterone receptor (PR), HER2 status, and the proliferation rate (Ki-67) are used to determine a surrogate (molecular-like) subtype. Within luminal(-like) IBC, no special subtype and invasive lobular breast carcinoma are the most common histological subtypes. Other rare histological subtypes (e.g., tubular carcinoma) should be recognized due to their distinct clinical and pathological features.

Keywords: Breast cancer; Estrogen receptor; Histological subtypes; Luminal A; Luminal B.

Fig. 1

Luminal-like invasive breast cancer of no special subtype (IBC NST) and rare patterns of IBC NST. A–C Histology of IBC NST, intermediate grade (G2): solid and tubular growth of carcinoma cells surrounded by stromal desmoplasia. Estrogen receptor (ER) expression is strong and homogeneous. A H&E. ×100. B H&E. ×400. C ER immunohistochemistry. ×200. D Glycogen-rich clear-cell pattern of IBC NST with predominantly clear cytoplasm due to accumulation of glycogen. D H&E. ×400. E, F Sebaceous pattern of IBC NST with typical characteristics of sebaceous cells with abundant and vacuolated cytoplasm. E H&E. ×100. F H&E. ×400.

Fig. 2

Patterns of invasive lobular breast carcinoma. A, B Histology of classical invasive lobular breast carcinoma (ILBC), intermediate grade (G2). Discohesive tumor cells are diffusely dispersed as single cells or grow loosely in a linear single-file pattern. A H&E. ×100. B H&E. ×400. C, D Pleomorphic ILBC, high grade (G3) with pleomorphic and hyperchromatic nuclei and increased mitotic activity. C H&E. ×100. D H&E. ×400.

Fig. 3

Rare histological subtypes of luminal breast cancer. A Histology of tubular carcinoma of the breast, low grade (G1). Tubular growth in >90% of the tumor, no marked pleomorphism of the nuclei and no increased mitotic activity. H&E. ×400. B Mucinous carcinoma with tumor cells floating in mucin. H&E. ×400. C In­vasive micropapillary breast carcinoma with morula-like tumor cell clusters surrounded by small sinus-like spaces. H&E. ×400. D Breast carcinoma with apocrine differentiation with granular eosinophilic cytoplasm. H&E. ×400. E Invasive breast cancer with neuroendocrine features including positivity for synaptophysin. H&E. ×400. F Synaptophysin immunohistochemistry. ×200.