ER/PR-positive invasive mucinous breast cancer: mastectomy, DIEP reconstruction, and tamoxifen

What happened, in summary

A 51-year-old trans woman was diagnosed with right breast multifocal invasive mucinous carcinoma after presenting in July 2022 with 1 month of fatigue and malaise. On examination, her doctor found a palpable, nontender breast mass without skin changes, nipple retraction, or discharge. Mammography and ultrasound showed a 2.9 × 2.0 × 1.9 cm lesion at the 2 o'clock position, 1 cm from the nipple. Core biopsy showed cT2N0 disease that was strongly hormone receptor-positive, with ER 100% positive, PR 100% positive, and HER2-negative results. A 19-gene hereditary cancer panel was negative, despite an extensive family history of cancer. She had been on estrogen therapy for 32 years as part of gender-affirming care and had not undergone genital surgery. After consultation with breast surgery, medical oncology, radiation oncology, and plastic surgery, she chose bilateral skin-sparing mastectomies with bilateral sentinel lymph node biopsies instead of lumpectomy with radiation. On 23 November 2022, she also had immediate bilateral DIEP free-flap reconstruction using abdominal tissue. Surgery and flap monitoring were uncomplicated, and she was discharged on postoperative day 6. Final pathology showed low-grade invasive mucinous carcinoma with a small DCIS component, negative sentinel nodes, and no lymphovascular invasion. Chemotherapy and radiation were not recommended. Because aromatase inhibitors were not appropriate in her setting, she chose 5 years of tamoxifen and started spironolactone after stopping estrogen. As of May 2024, she was 1 year after reconstruction, pleased with the results, and planning nipple reconstruction and tattooing. At 2-week follow-up, she had mild breast, axilla, and arm discomfort but was otherwise well and able to perform daily activities.