Synchronous triple-negative breast cancer and rectal adenocarcinoma complicated by hepatitis B reactivation

What happened, in summary

This 55-year-old Arab woman, a married mother of 5, presented with a rapidly enlarging painful mass in her right breast. She had noticed a smaller stable mass in the same breast for about 10 years, but the new growth was associated with skin dimpling and nipple retraction. Mammography and CT showed a 5 x 4 cm heterogeneous solid and cystic central breast mass with skin thickening and small axillary nodules, but no distant metastases. Core biopsy confirmed invasive ductal carcinoma that was triple-negative: ER-negative, PR-negative, and HER2/neu-negative. Genetic testing reported a pathogenic BRCA1 mutation. She started neoadjuvant weekly paclitaxel plus carboplatin with pembrolizumab every 3 weeks, planned for 6 cycles. The early cycles caused only mild fatigue and nausea, but before cycle 5 she developed severe transaminitis and a sharp rise in hepatitis B virus levels, confirming hepatitis B reactivation. Chemotherapy was stopped, and entecavir 0.5 mg daily was started. Within 4 weeks, liver enzymes normalized and HBV DNA became undetectable. During the same overall course, rectal bleeding led to diagnosis of a separate mid-rectal invasive adenocarcinoma. She underwent right modified radical mastectomy for breast cancer and rectal resection with colostomy for rectal cancer. Pathology confirmed 2 distinct primary tumors. Later PET findings raised concern, but follow-up biopsies did not show recurrence. She completed adjuvant radiation. At 3-year follow-up, she remained healthy and disease-free while continuing long-term antiviral management. Her course required coordination across breast oncology, colorectal surgery, infectious disease, genetics, and radiation therapy because cancer treatment and viral reactivation had to be managed together.