A 45 years old female with well circumscribed recently palpated 1.5 cm right breast mass. suspicious on imaging
 

Contributed By:   Kamaljeet Singh MD

 

Please choose:

  • Metaplastic carcinoma with squamous component

  • Infiltrating ductal carcinoma, NOS

  • Malignant adenomyoepithelioma

  • Invasive carcinoma with apocrine features

 

 

 

 

The answer is Metaplastic carcinoma with squamous component.

Discussion:

Metaplastic carcinoma with squamous carcinoma component

The tumors consist of invasive carcinoma with a central dense fibrotic/collagenous area. The tumor cells display overt squamous differentiation, evident by abundant eosinophilic cytoplasm. Tumor is populated by cytoplasm-poor basaloid cells which are interspersed in a myxoid matrix (last picture) suggesting a component of matrix producing metaplastic carcinoma. Some tumor cells have a plasmacytoid cytology in this focus. The tumor will be best classified as mixed metaplastic carcinoma.

Current blue book on breast tumors (WHO, 2019) acknowledges that metaplastic carcinoma is a heterogeneous group where tumor cells differentiate towards squamous and /or mesenchymal-appearing elements. Although pure forms of metaplastic carcinomas are often discussed (low grade adenosquamous, fibromatosis-like, spindle cell, squamous, and metaplastic with heterologous mesenchymal diff), a large proportion of metaplastic carcinomas displays a mixture of aforementioned pure elements, as well as metaplastic and conventional adenocarcinoma elements.

Metaplastic carcinomas constitute 0.2-1% of all breast cancers. They are often triple negative and larger in size than IDC, NST. Histologic subtyping is relevant, since, low-grade adenosquamous carcinoma and fibromatosis-like metaplastic carcinoma tend to have indolent behavior and matrix producing carcinomas are associated with better prognosis. Although WHO recommends providing proportion of each elements in the mixed metaplastic carcinoma, however it is unclear if it is currently practiced.

Reference: WHO classification of Tumours Editorial Board. Breast tumours. Lyon (France): IARC; 2019 (page 134-138).