HR-positive HER2-negative metastatic breast cancer: bone metastases managed with sequential endocrine therapy

What happened, in summary

A 58-year-old post-menopausal woman presented with 1 month of progressive neck pain, a growing breast mass, and a non-itchy red rash over the breast and abdomen. Examination found a hard, immobile breast mass with multiple enlarged axillary lymph nodes. Imaging showed a large hypermetabolic breast mass, axillary nodal disease, and extensive bone metastases involving the skull base, spine, sternum, ribs, left iliac bone, and right inferior pubic ramus. The T1 vertebra had completely collapsed and was compressing the subarachnoid space and spinal cord. Biopsy showed invasive mammary carcinoma with ductal carcinoma in situ and comedo necrosis. Biomarkers were ER 90% positive, progesterone receptor 80% positive, and HER2 negative. CA 15-3 was elevated at 45.47 IU/mL. First-line treatment used letrozole 2.5 mg daily, zoledronic acid every 4 weeks, and palliative radiotherapy. After about 7 months, PET/CT showed a 30% partial response, including shrinkage of the breast lesion and decreased bone-lesion activity. Later, after new L4 disease and persistent sternum activity, letrozole was changed to tamoxifen with zoledronic acid, but PET/CT showed mild progression and CA 15-3 rose to 57.33 IU/mL. She underwent hysterectomy with bilateral salpingo-oophorectomy after post-menopausal bleeding and possible fibroid findings. Letrozole was restarted with fulvestrant and zoledronic acid, but liver-test abnormalities and gallbladder disease occurred, and the sternum lesion continued to progress. Treatment was then changed to palbociclib 125 mg daily for 21 days on and 7 days off, fulvestrant every 28 days, and zoledronic acid every 3 months. After 3 months, PET/CT showed stable disease; 1 year later, multiple bone lesions remained stable and non-hypermetabolic, described as remission. She continued follow-up every 3 months while managing neutropenia and jaw osteonecrosis.