Symptomatic bone marrow involvement by metastatic occult HR+/HER2- breast cancer treated with ribociclib and letrozole: A case report.

Visceral crisis (VC) occurs in less than about 15% of patients with de novo metastatic breast cancer (BC). We present a case of a 59-years-old woman who presented with history of bone pain, fatigue, dyspnea on exertion, and weight loss; on physical examination was found no breast nodules, enlarged lymph nodes, or enlarged viscera were palpable. Laboratory tests revealed hemoglobin 5.8 g/dl. PET CT scan showed multiple osteolytic lesions. A bone marrow biopsy was performed, which identified infiltration by an epithelial tumor lesion. Immunohistochemistry showed positivity for CK1/3, CK7, Gata-3, and estrogen and progesterone receptors. HER2 negative (0+). The diagnosis of de novo occult HR+/HER2- metastatic BC was made. Systemic treatment with ribociclib and letrozole was started; the patient experienced clinical improvement of the symptoms, weight gain and improvement in hemoglobin levels. VC in HR+/HER2- metastatic BC is a challenging situation from its definition to its management. In case of availability and quick access, a free CT regimen with CDK4/6i + endocrine therapy could be a option to consider in this patients. This also represents a challenge in terms of cost-effectiveness in the health systems of low-income countries.