Supplementary Material for: Sequential Diagnosis of Metastatic Breast Cancer and Follicular Lymphoma in a Postmenopausal Woman: Navigating Endocrine and Cytotoxic Therapies in a Complex Oncologic Setting

Introduction: Dual primary malignancies involving solid and hematological tumors are rare, posing significant diagnostic and therapeutic challenges. We report here a case of concurrent breast cancer and follicular lymphoma. Case Presentation: A 52-year-old woman with hormone receptor-positive early-stage breast cancer (pT2N2a) developed pleural metastasis concurrently with newly diagnosed follicular lymphoma (Ann Arbor stage IIIA, Grade 1-2) at 3 years postdiagnosis. The lymphoma progressed during treatment for metastatic breast cancer. Consequently, treatment was switched to combination immunochemotherapy with rituximab, cyclophosphamide, vincristine, and prednisolone (R-CVP). The patient achieved a partial response for follicular lymphoma, without breast cancer progression. Endocrine therapy with letrozole and palbociclib was successfully resumed following bone marrow recovery. Conclusion: This case highlights the need to consider secondary malignancies during cancer treatment and demonstrates the clinical utility of R-CVP in the management of dual cancer.