Abstract PS3-10-02: Factors influencing the number of adjuvant TC - docetaxel and cyclophosphamide - cycles in hormone receptor-positive early-stage breast cancer

Abstract Introduction Docetaxel and cyclophosphamide (TC) is a widely used anthracycline-free regimen for hormone receptor-positive (HR+) early-stage breast cancer. While typically administered over four to six cycles, the optimal number of cycles for various risk profiles remains a topic of clinical debate. This study aimed to identify clinical and pathological factors associated with the number of adjuvant TC cycles prescribed in a real-world setting. Methods We conducted a retrospective analysis of patients with HR+ early-stage breast cancer treated between 2018 and 2025 across a multicenter oncology network in Brazil. Eligible patients had undergone surgery and received adjuvant TC chemotherapy. Variables such as age, menopausal status, tumor size and nodal status, histologic grade, and Ki-67 index were examined in relation to the number of TC cycles administered (six versus four). For patients who received four cycles, we recorded whether this was based on the original treatment plan, early discontinuation due to adverse events, or other reasons. Logistic regression was used to evaluate associations between baseline characteristics and the likelihood of receiving fewer versus more TC cycles. Results A total of 372 patients who received adjuvant TC were evaluated; 206 (55.4%) received four cycles and 166 (44.6%) received six cycles. Among those receiving four cycles, the majority (87.9%) had this number planned at the outset. Only four patients (1.9%) had the number of cycles reduced due to treatment-related toxicities. The reason for choosing four cycles was not documented in the remaining 10.2%. Patients who received six cycles were slightly younger (median age 50 years [range 27-81]) than those receiving four cycles (median age 52 years [range 29-83]; P=0.025). The six-cycle group had a higher proportion of patients with positive lymph nodes (42.2% pN1 and 3.6% pN2) compared to the four-cycle group (19.9% pN1 and 0.9% pN2; P