Clinicopathological Analysis of Ten Patients with Metaplastic Squamous Cell Carcinoma of the Breast

Purpose. Primary squamous cell carcinoma (SCC) and metaplastic squamous cell carcinoma (MSCC) are rare types of breast cancer with specific histological features. They are characterized by rapid progression, a tendency toward cyst formation, and negativity for hormone receptors. Many studies have concluded that SCC of the breast carries a poor prognosis, based on the fact that conventional chemotherapy for ductal carcinoma of the breast is ineffective against SCC. This is a retrospective study of patients in a single center with SCC or MSCC. Methods. We searched the records of the Tokyo Metropolitan Komagome Hospital for patients diagnosed with breast SCC or MSCC between 1979 and 2006. Squamous cell carcinoma was diagnosed when 100% of the malignant cells showed a squamous component (pure SCC) and MSCC was diagnosed when more than 50% of the malignant cells showed a squamous component. We analyzed the clinicopathological features, treatment methods, and outcomes of these patients. Results. We identified 10 (0.28%) patients with SCC or MSCC from among 3565 patients with malignant breast tumors treated at our hospital during this period. Nine patients had adenocarcinoma with squamous metaplasia, and one had pure SCC. Ultrasound showed a central cystic-necrotic component in seven tumors, and all of the tumors were negative for hormone receptors and HER2. Recurrence developed in two patients with lymph node metastasis, but not in the other eight patients. The 5-year survival rate and median survival time were 85.7% and 97 months, respectively. Conclusions. Squamous cell carcinoma or MSCC of the breast with features of the triple-negative subtype seems to be associated with a poor prognosis; however, node-negative patients are likely to have a favorable prognosis.