Multiple breast tumors coexisting with chronic lymphocytic leukemia/small lymphocytic lymphoma: a rare case report.

Concurrent presentation of multiple breast carcinomas with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is exceptionally rare in clinical practice. This report presents the case of a 77-year-old woman with two distinct right breast carcinomas. The patient underwent neoadjuvant carboplatin/paclitaxel chemotherapy with pembrolizumab, achieving partial radiologic response. Following neoadjuvant therapy, the patient underwent right breast mastectomy with sentinel lymph node biopsy, which was positive, prompting subsequent axillary lymph node dissection. Post-mastectomy pathology revealed residual ductal carcinoma with marked treatment effect, persistent lobular carcinoma, and multifocal CLL/SLL infiltration in breast tissue with metastasis to axillary lymph nodes. The final staging was ympT1c N1a and the patient recommended for adjuvant pembrolizumab plus capecitabine with radiotherapy for breast carcinoma and surveillance with positron emission tomography-computed tomography for CLL. The outcome underscores the importance of meticulous histopathological and immunohistochemical evaluation in distinguishing concurrent malignancies from metastatic or reactive lymphoid infiltrates.