Rare squamous cell breast cancer: tumorectomy and partial mastectomy

What happened, in summary

This 49-year-old woman noticed a new lump in her left breast in July 2021. Screening breast ultrasound 9 months earlier had shown no abnormalities, so the rapid appearance of a 30 mm mass prompted further evaluation. Physical examination found a mobile 30 mm mass in the outer left breast. Mammography, MRI, and ultrasound showed a well-defined mass, and the initial ultrasound-guided biopsy was interpreted as fibroadenoma. Because the mass had grown quickly, she underwent left tumorectomy in September 2021. Pathology changed the diagnosis: the mass contained well-differentiated squamous cell carcinoma with 9 mm stromal invasion arising within a benign phyllodes tumor. The cancer was ER-negative, PR-negative, HER2-negative, with Ki-67 of 21%, and the margins from the first excision were negative. A separate lesion near the margin raised concern for LCIS or DCIS, but continuity with the squamous cell carcinoma was not confirmed. PET/CT after surgery showed no abnormal uptake, helping rule out metastasis to the breast from another organ. This mattered because primary squamous cell carcinoma of the breast is rare, and squamous tumors more often originate elsewhere. The tumor was staged T1bN0M0, Stage I. She then had partial left mastectomy, also described as additional excision, with sentinel lymph node biopsy for final surgical staging. Adjuvant treatment included 4 courses of AC chemotherapy with doxorubicin and cyclophosphamide, followed by 4 courses of docetaxel. She also received residual breast irradiation, 50 Gy in 25 fractions. As of August 2024, she remained under observation with no recurrence 4 years after surgery.