Stage IIIB HER2-positive breast cancer followed by resected pancreatic ductal adenocarcinoma

What happened, in summary

A 54-year-old woman presented in June 2017 with a painless left breast mass that had grown over 6 months. Ultrasound and MRI showed a BI-RADS 5 breast mass, skin thickening, and multiple enlarged axillary lymph nodes. Core biopsy on June 14, 2017 confirmed invasive ductal carcinoma. The breast cancer was clinically staged as T3N2M0, Stage IIIB. Initial testing showed ER positivity at 40%, PR positivity at 40%, and HER2 gene amplification by FISH. She received 3 cycles of neoadjuvant TAC chemotherapy with docetaxel, epirubicin, and cyclophosphamide every 21 days. On August 15, 2017, she underwent left modified radical mastectomy. Pathology showed a 6.0 cm tumor with cancer in 4 of 14 axillary lymph nodes. After chemotherapy, the tumor had lost ER and PR expression but retained HER2 overexpression at 3+, with p53 overexpression. She completed 3 more TAC cycles, 25 fractions of radiotherapy, and 1 year of trastuzumab. Toremifene was started but then held because the surgical specimen was ER-negative. She entered regular surveillance with radiological and clinical remission. In 2025, an elevated CA19-9 led to imaging that found a 2.0 cm pancreatic uncinate-process mass. Whipple surgery on July 16, 2025 confirmed a separate pancreatic ductal adenocarcinoma, not breast metastasis. Postoperative recovery was uneventful, and adjuvant gemcitabine plus albumin-bound paclitaxel was recommended. Pathology from the pancreatic operation was CK7-, CK19-, DPC4/SMAD4-, and MUC1-positive, while GATA3 and GCDFP-15 were negative, supporting a new pancreatic primary rather than metastatic breast cancer. Germline testing found no pathogenic BRCA1, BRCA2, PALB2, or ATM variant.