Stable Stage IV breast cancer after a serious side effect from abemaciclib

What happened, in summary

A premenopausal woman in her 50s was investigated for persistent anemia. A bone marrow biopsy unexpectedly showed breast-cancer cells, and further testing found cancer in both breasts with spread to the bone marrow. Both tumors were hormone-receptor positive and HER2-negative, and the disease was Stage IV.

She started ovarian suppression and an aromatase inhibitor together with abemaciclib. Early treatment was manageable, but her white blood cell count later fell and abemaciclib had to be paused temporarily.

About 2.5 months after starting treatment, she developed severe abdominal pain, fever, and profound neutropenia. Imaging showed inflammation of the ascending colon, consistent with neutropenic enterocolitis. Her blood pressure dropped sharply, and she required intensive-care treatment with antibiotics, supportive medication, and medication to help her white blood cell count recover. She improved quickly and left the hospital after 10 days.

Abemaciclib was later restarted at a lower dose. About 2 years after her original treatment began, she remained on therapy without disease progression and her condition was stable.