Abstract
<title>Abstract</title> <p>Background The use of Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors in the treatment of hormone-positive metastatic breast cancer has led to an increase in disease-free survival. Neutropenia is the most common side effect of this group of drugs and its occurrence at different times in each patient may have prognostic significance. Materials and Methods The data of metastatic breast cancer patients who admitted between January 2020 and December 2023 were retrospectively reviewed. 67 patients were included in the study. Among the patients who used ribociclib in addition to endocrine therapy in the first or second series, female patients were included in the study who did not have any biochemical side effects other than neutropenia. The times were determined when neutropenia occurred. Results The mean age at diagnosis of 67 female patients was 53.22 ± 11.02 years. Twenty-eight of the patients had metastases in a single site and 39 had metastases in two or more sites. Progression-free survival (PFS) was longer in patients with single-site metastases. PFS was shorter in patients who developed neutropenia in the first 3 months (χ²=13,769; sd = 2; p = 0,001). Patients who developed neutropenia below 1000 during ribociclib use were found to have a shorter PFS. (χ²=12,932; sd = 2; p = 0,002). When the estrogen receptor level, progesterone receptor level, Ki67 and PFS levels were compared, no statistically significant difference was found (p > 0.05). PFS was longer in patients with cerbB2 score 1 + than in those with score 2+ (p = 0.005). No effect of NLR (neutrophil/lymphocyte ratio) measured before treatment on PFS was detected. Conclusion Neutropenia occurring during the use of ribociclib, a CDK 4/6 inhibitor, affects the duration of advanced breast cancer treatment and the occurrence of neutropenia may be a prognostic indicator. Survival analyses have shown significant associations between neutropenia severity and timing and PFS.</p>