Adaptive Surgical Decision-Making for Synchronous Metastatic Pancreatic Cancer and Early Breast Cancer with a BRCA1 Pathogenic Variant: A Case Report.

Synchronous pancreatic and breast cancers associated with a breast cancer susceptibility gene (BRCA)1 pathogenic variant are extremely rare. When 1 malignancy presents as stage IV disease, determining the optimal timing and extent of surgical intervention for a second primary cancer represents a major clinical challenge. A woman in her 60s was diagnosed with synchronous stage IV pancreatic tail cancer with multiple liver metastases and stage I left breast cancer. S-1/oxaliplatin/irinotecan (SOXIRI) was initiated for metastatic pancreatic cancer, achieving a sustained partial response. Germline testing revealed a BRCA1 pathogenic variant. Maintenance olaparib was subsequently introduced, resulting in durable disease stabilization and normalization of tumor markers. While the pancreatic cancer remained controlled, the breast cancer progressed with axillary lymph node involvement. After confirming long-term systemic stability and preserved performance status, breast-conserving surgery with level II axillary lymph node dissection was performed 28 months after treatment initiation. At 77 months, the patient remains alive without breast cancer recurrence or pancreatic cancer progression. Adaptive surgical decision-making for a concurrent operable malignancy, supported by durable systemic control of a dominant stage IV cancer, may help prevent the malignancy from becoming an additional threat to long-term prognosis. Dynamic reassessment of oncologic priority is essential in the era of molecularly targeted therapy.