First-line endocrine therapy combined with CDK 4/6 inhibitor in disseminated carcinomatosis of bone marrow (DCBM) luminal breast cancer: a case report.

Background: Metastatic breast cancer especially in disseminated carcinomatosis of bone marrow (DCBM) poses a life-threatening risk, often requiring systemic chemotherapy. This situation lacks a cure, emphasizing symptom relief and quality of life. The documented occurrence of DCBM is merely 0.17% in metastatic breast cancer and ranges from 0.6 to 1.7% in solid tumors. Until now, there is no official medical guideline for treating patients with luminal breast cancer (LBC) who have DCBM. This case report highlights LBC patient with DCBM, treated at diagnosis with first-line therapy combining endocrine therapy (ET) and a CDK4/6 inhibitor.

Case presentation: A 36-year-old premenopausal female of Javanese ethnicity with advanced de novo luminal breast cancer diagnosed in 2020. The immunohistochemistry showed estrogen receptor (ER)+ (90%), progesterone receptor (PR)+ (20%), human epidermal growth factor receptor 2 (HER-2) negative, and a high Ki-67 staining result at 60%. The patient had visceral crisis, which involved bone marrow infiltration and liver metastasis with preserved liver function. After intolerance of side effects from first line treatment with tamoxifen, the treatment plan was adjusted to letrozole, ribociclib, and leuprorelin injection. After completing the sixth cycle of treatment, blood parameters in the laboratory were found to have returned to normal. The patient's response to this regimen was remarkable, with significant alleviation of symptoms and improvement in quality of life observed.

Conclusion: Notably, the combined approach of ET and CDK4/6 inhibitor represents a novel intervention in managing DCBM in patients with LBC.