A Case of Metaplastic Squamous Cell Carcinoma of the Breast that Showed a Pathological Complete Response After Neoadjuvant Chemotherapy with Weekly Paclitaxel.

BACKGROUND Primary squamous cell carcinoma of the breast is a rare type of metaplastic breast carcinoma, characterized by resistance to conventional chemotherapy agents. We report a case of metaplastic squamous cell carcinoma of the breast in which a pathological complete response was achieved after neoadjuvant chemotherapy with weekly paclitaxel and in which the patient remained disease free for 15 years and 7 months. CASE REPORT A 40-year-old woman had a palpable 5-cm-diameter tumor in the right breast that was diagnosed as metaplastic squamous cell carcinoma of the breast based on core needle biopsy. The patient was initially treated with an adjuvant chemotherapy (AC) regimen consisting of doxorubicin (60 mg/m²) and cyclophosphamide (600 mg/m²) as neoadjuvant chemotherapy. Because the tumor grew rapidly and the skin redness increased after 1 cycle of the AC regimen, 12 cycles of weekly paclitaxel 80 mg/m² were subsequently administered. The tumor responded dramatically to paclitaxel. The patient underwent mastectomy with level II axillary lymph node dissection. No residual tumor cells were found, which indicated pathological complete response. The patient is currently disease free at 15 years and 7 months after the operation. CONCLUSIONS To our knowledge, there are no previous reports of metaplastic squamous cell carcinoma of the breast in which pathological complete response was achieved by treatment with neoadjuvant chemotherapy with weekly paclitaxel (80 mg/m²).