EARLY CHEMOTHERAPY-INDUCED NEUTROPENIA AS A PREDICTOR OF TUMOR RESPONSE IN BREAST CANCER PATIENTS RECEIVING NEOADJUVANT CHEMOTHERAPY

Background. Neoadjuvant chemotherapy (NACT) is an essential component of comprehensive treatment for locally advanced and biologically aggressive breast cancer. However, individual sensitivity to cytotoxic therapy varies considerably. Chemotherapy-induced neutropenia has traditionally been regarded as an adverse event requiring careful monitoring and, in some cases, chemotherapy dose adjustments or the administration of granulocyte colony-stimulating factor (G-CSF). Nevertheless, early hematological toxicity may indirectly reflect adequate systemic exposure to cytotoxic agents and may potentially be associated with tumor response to treatment. Objective. To evaluate the association between early chemotherapy-induced neutropenia and the effectiveness of neoadjuvant chemotherapy in patients with breast cancer. Materials and Methods. The study included 92 patients with stage II–III breast cancer who received neoadjuvant systemic chemotherapy followed by surgical treatment. Depending on the development of grade 2–3 neutropenia during the initial chemotherapy cycles, the patients were divided into two groups. Group I consisted of 47 patients who developed early neutropenia, while Group II included 45 patients without clinically significant neutropenia. Clinical tumor response, the rate of pathological complete response (pCR), changes in primary tumor size, treatment delays, chemotherapy dose reductions, and major adverse events were evaluated. Results. A pathological complete response was achieved in 20 patients (42.6%) in Group I and 11 patients (24.4%) in Group II. The mean reduction in primary tumor size was 69.1% and 54.8%, respectively. The association between early neutropenia and tumor response was particularly pronounced in patients with triple-negative and HER2-positive breast cancer. However, severe hematological toxicity resulting in prolonged treatment interruptions was associated with a higher frequency of chemotherapy dose reductions. Conclusion. Early moderate chemotherapy-induced neutropenia may be associated with a more pronounced tumor response to neoadjuvant chemotherapy. However, severe or prolonged neutropenia may negatively affect treatment continuity. Individualized hematological monitoring and timely supportive care are essential to maintaining an appropriate balance between treatment efficacy and safety.