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Efficacy Of CDK4/6 inhibitors in hormone-dependent breast cancer with bone marrow infiltration – real world data from UHC Zagreb

Introduction: The combination of CDK4/6 inhibitors and endocrine therapy (ET) prolongs survival in patients with HR+/HER2-metastatic breast cancer (mBC). Patients with bone marrow infiltration (BMI) often have low blood count parameters and are therefore an underrepresented group in CDK 4/6 inhibitor registration studies. The trial inclusion criteria include adequate haematopoiesis -absolute neutrophil count ≥ 1.5 × 10^9 / L, platelet count ≥ 100 × 10^9 / L and haemoglobin ≥ 9.0 g / dL. This study analysed the response totherapy and the time to treatment failure (TTF), defined as the interval from therapy initiation to premature discontinuation, in order to determine the safety and efficiency of thetreatment. Methods: Retrospectively, data from the hospital information system for 203 patients, treated with a combination of CDK 4/6 inhibitors and ET with the medianfollow-up of 12 months (1–32 months) was analysed. 16 patients (7.88%) had proven BMI and were analysed separately. Age, endocrine sensitivity, number of previous treatment lines and TTF were determined in this group. Result: The median age was 49.5 (34–78 years). 8 patients had de novo metastatic disease. At the start of treatment, 4 patients (25%) were endocrine- sensitive. CDK 4/6 inhibitors were a first-line treatment in 5 patients (31.25%), 2nd in 7 (43.75%), 3rd in 3 (18.75%) and 4th in one patient (6.25%). All patients treated in the first-line are still receiving the treatment with therapy duration of 3– 19 months. 9 patients (56.25%) with BMI reached TTF and their median TTF is 6 months (2–12). Conclusion: Observing the effects of CDK4/6 inhibitor treatment in patients with HR+ /HER2– mBC with BMI is important because in this subgroup, in everyday clinical practice, we frequently opt for chemotherapy due to the fast onset of action, and also because many consider bone marrow infiltration a manifestation of a visceral crisis. With transfusion support and close monitoring, response to treatment with CDK4/6 inhibitors and disease regression have been reported in most patients in the first-line of treatment, as well as in some patients treated in the subsequent lines. CDK 4/6 inhibitors can significantly affect the quality of life in this subgroup of patients by delaying the start of chemotherapy.

bone marrow involvement ; CDK4/6 ; breast cancer

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