Kosin Med J.  2022 Sep;37(3):176-186. 10.7180/kmj.22.022.

Mucinous carcinoma of the breast: distinctive histopathologic and genetic characteristics

• Jung M

• KMID: 2538796
• DOI: http://doi.org/10.7180/kmj.22.022

Abstract

Mucinous carcinoma is a rare histologic type of breast cancer that, when classified with favorable histology, can be treated with different therapeutic options. This study reviews the histologic findings of mucinous carcinoma that support or exclude favorable histology and emphasizes the necessity of an appropriate gross examination with radiologic findings for an accurate diagnosis. In addition, unusual findings such as micropapillary arrangements and lobular differentiation in mucinous carcinoma and their implications for prognosis and treatment are reviewed. Mucinous carcinoma involves upregulation of MUC2, a mucus-associated gene common in mucinous carcinoma of the breast as well as various other organs. In mucinous carcinoma, the fraction of genome altered and tumor mutation burden are lower than those of invasive carcinoma of no special type, the most common histology of breast cancer. In addition, the genetic alterations found in mucinous carcinoma are diverse, unlike the pathognomonic genetic alterations observed in other histologic types of breast cancer. These genetic features support the importance of conventional microscopic evaluations for the pathologic differential diagnosis of mucinous carcinoma of the breast in routine practice. A variety of breast lesions, including mucinous cystadenocarcinoma and mucocele-like lesions, as well as mucinous carcinoma from other organs, can mimic mucinous carcinoma of the breast. In order to obtain an accurate pathologic diagnosis, careful evaluation of the overall histopathologic characteristics and ancillary testing are required to provide information on appropriate treatment and prognosis.

Keyword

Breast; Diagnosis, differential; Mucinous carcinoma; Prognosis

Figure

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  Fig. 1. A comparison of mucinous carcinoma of the breasts (MCBs) with different cellularity. (A) Type A MCB is characterized by a small number of tumor cells forming small clusters and a background of abundant extracellular mucin (H&E, ×100). (B) Type B MCB is characterized by hypercellular tumor cells forming large clusters. The mucinous background between the clusters is relatively poor compared to that of type A (H&E, ×100).

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  Fig. 2. Mucinous carcinoma of the breasts (MCBs) with micropapillary features. (A) Tight morula-like clusters of intermediate to high-grade tumor cells are floating within the small spaces filled with extracellular mucin (H&E, ×200). (B) Mucus filling the spaces between the tumor cells and the surrounding stromal tissue is identified by Alcian blue staining (×200). (C) Immunohistochemical staining for epithelial membrane antigen is observed on the stromal-facing peripheral membrane of the tumor cells, clearly revealing the inside-out pattern (×200). (D) Abundant intracytoplasmic vacuoles are found in the focal area of MCB with micropapillary features (H&E, ×400).

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  Fig. 3. Mucinous carcinoma of the breasts (MCBs) with lobular differentiation. Single tumor cells with low nuclear grade float within the mucin pool. The presented lobular differentiation is a focal finding in a case of mixed MCB (H&E, ×200).

Reference

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