What happened, in summary

A 74-year-old woman had been followed for an indolent blood disorder that later became Waldenström’s macroglobulinemia. In 2018, a bone-marrow biopsy unexpectedly found ER-positive epithelial cancer cells consistent with breast origin. Mammography, ultrasound, and breast MRI could not identify a primary breast tumor, but the marrow finding established occult metastatic breast carcinoma.

She began first-line endocrine therapy with an aromatase inhibitor and remained clinically stable for several years. In September 2024, new diffuse bone pain and imaging showing multiple skeletal lesions indicated progression of the breast cancer. A repeat bone biopsy again showed metastatic breast carcinoma within marrow that also contained the separate lymphoid malignancy.

In December 2024, treatment changed to palbociclib plus fulvestrant. Subsequent imaging in 2025 showed stable skeletal lesions, while tumor markers declined. At the most recent follow-up in March 2026, the skeletal disease remained stable and biochemical measures continued to improve. This represents more than seven years living with metastatic breast cancer from its first identification in 2018, while the coexisting blood cancer was monitored separately.