Case Report Metaplastic Carcinoma of the Breast with Squamous Differentiation: A Case Report from the University Teaching Hospital of Kigali (CHUK), Rwanda Delphine Uwamariya , 1 Carine Nyampinga, 1 Anne Yvette Nsenguwera, 2 and Belson Rugwizangoga 1,2 1 Department of Clinical Biology, School of Medicine and Pharmacy, University of Rwanda, Kigali, Rwanda 2 Department of Pathology, University Teaching Hospital of Kigali, Kigali, Rwanda Correspondence should be addressed to Delphine Uwamariya; uwamariya94@gmail.com Received 26 November 2019; Revised 28 July 2020; Accepted 6 August 2020; Published 29 August 2020 Academic Editor: Piero Tosi Copyright © 2020 Delphine Uwamariya et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Metaplastic breast carcinoma is a rare and aggressive condition, accounting less than 1% of breast malignancies. It presents with large mass and frequently with distant metastasis at time of diagnosis. Morphologically, it is characterized by the differentiation of neoplastic epithelium into epithelial or mesenchymal-looking elements like squamous cells, spindle cells, cartilage, or bone and has poor prognosis with its triple negative status. 1. Introduction Metaplastic carcinoma of the breast is a rare condition that accounts for less than 1% of breast malignancies. They are aggressive tumors that have a worse prognosis than other tri- ple negative invasive ductal carcinomas [1, 2]. Metaplastic carcinomas of the breast are characterized by large tumor size and rapid growth and have a high potential for metastatic spread to the lung and bone via vasculature rather than by way of lymphatics [3]. Morphologically, they are character- ized by neoplastic epithelial or mesenchymal differentiation. Of the epithelial variant, the squamous cell carcinoma is the most common. Those with mesenchymal differentiation can present with proliferation of spindle cells, cartilage, or bone. Metaplastic carcinomas frequently present as well- demarcated tumors and therefore have many similarities with some variants of invasive ductal carcinoma and also with benign lesions on mammography [3]. Treatment for metaplastic breast carcinoma is relatively unknown because of the rarity of the disease, but studies suggest that the removal of the tumor and adjuvant radiation therapy has the greatest impact [3]. In this paper, we report a case of squamous metaplastic carcinoma, diagnosed in Rwanda. 2. Case Report A 39-year old female patient had a 2-year history of left breast mass that measured 4×3×2:5 cm by clinical exami- nation; imaging information is not available. An attempt to excise the mass was done at the district hospital; the histopathological examination reported it to be a poorly differentiated ductal carcinoma with cystic degeneration (immunohistochemistry results and information on the margin status are not available). The tumor recurred 6 months after the initial surgery. At this point, she was referred to a tertiary hospital where she underwent modified radical mastectomy; the specimen was submitted for histo- pathology examination. On gross examination, the mastectomy weighed 300 g and measured 16 × 16 × 7 cm. The axillary tail measured 8 cm in length. The ellipsoid skin flap measured 12 × 9 cm and dem- onstrated an everted, grossly unremarkable nipple. On serial sections, the specimen shows a cystic lesion (3.5 cm in the greatest dimension) in the lower inner quadrant of the breast. The cystic cavity was filled with hemorrhagic fluid and necrotic debris. Grossly, the tumor was at 0.2 cm from the deep margin and 1.1 cm from the anterior-inferior margin. Hindawi Case Reports in Pathology Volume 2020, Article ID 4806342, 3 pages https://doi.org/10.1155/2020/4806342