Abstract PO5-02-14: Clinical-pathological determinant factors to choose between four or six cycles of adjuvant chemotherapy with docetaxel/cyclophosphamide (TC) in a retrospective real-world cohort of HER2-negative breast cancer patients

Abstract

Abstract Introduction: The long-term severe adverse events associated with anthracyclines, including irreversible cardiotoxicity, myelodysplastic syndromes, and therapy-related leukemias, led researchers to question the risk-benefit of anthracycline-based chemotherapy regimens, especially for patients without axillary lymph node involvement, leading to an increasing trend to omit anthracyclines in adjuvant treatment. Docetaxel plus cyclophosphamide (TC) has replaced doxorubicin plus cyclophosphamide (AC) for lower-risk patients that need adjuvant chemotherapy. However, the optimal number of cycles of adjuvant in patients with node-positive or node-negative breast cancer is currently unknown. Methods: We performed a retrospective cohort study of patients with HER2-negative breast cancer, stage I to III, that received adjuvant docetaxel and cyclophosphamide (TC) for four or six cycles, treated from January 2010 to December 2021. Patients were included from four cancer institutions, both private and public, located in the South, Southeast, and Northeast of Brazil. Objectives: To investigate the clinical-pathological characteristics and survival of earlystage HER2-negative breast cancer patients who received four (TC4) or six cycles (TC6) of adjuvant docetaxel and cyclophosphamide (TC). Results: We collected data from six hundred and ninety-eight patients, 98.7% were female with an average age of 52 years, 51.9% were postmenopausal, 14.6% BRCA gene mutation, 66% had some comorbidity, and only 8.4% were not candidates for anthracyclines. Two hundred and twenty-five patients had public and 473 private health insurance. About 13.2% of the patients were hormone receptor negative (HR-) and 86.8% hormone receptor positive (HR+), 57.4% breast-conserving surgery and 77.7% sentinel lymph node (SL). Five hundred sixty-four (80.8%) patients received TC4 and 134 (19.2%) TC6. We observed that patients who received TC 6 had unfavorable prognostic factors such as: (TC4 vs TC6) previous breast cancer (8.7% vs 16.3%) (p=0.002), invasive ductal carcinoma (IDC) (73.4 vs 86.7%) (p=0.009), histological grade 3 (HG3) (34.9 vs 42.9%) (p= 0,085) conservative surgery (59.4% vs 53%) (p=0144), SL (80.9% vs 62.2%) (p =0.001), Lymph node positive (15% vs 42.3%) (p=0.001), pathological stage II (37.5% vs 50%) (p=0.001).Treatment completion rates were 96.5% and 84.3% for TC4 and TC6, respectively (p=0,02). The incidence of grade 3 or higher toxicity with TC6 (14% vs 21.1%; p= 0,043). Febrile neutropenia was observed in 6.7% of both groups. Grade 3 or higher neuropathy was most common with TC6 (2.2% vs 10.3%; p=0,163). Permanent treatment discontinuation was more frequent in the TC6 group (3.4% vs. 9.8%; p=0,004), as well as late toxicity (3.4% vs. 9.2%; p=0,004). Ninety-four percent of the patients completed the proposed cycles of chemotherapy, 72% received adjuvant radiotherapy and 85.4% received adjuvant hormone therapy, with 42% of these receiving an aromatase inhibitor for 5 years. The median follow-up of the entire cohort was 61 months. There was no difference in the 5-year DFS (77.5% vs. 64.7%; p=0.159) or the 5-year OS (89.5% vs. 70.5%; p= 0,06) between patients treated with TC4 and TC6. Conclusion: TC6 was commonly used for patients with unfavorable prognostic factors as history of previous breast cancer, (IDC), HG III, lymph node positive and stage II. Patients who received TC6 had less chance of completing the treatment and more severe toxicity, especially late peripheral neuropathy. There was no difference in DFS or OS. Citation Format: Mila Kraychete, Marcelle Cesca, Guilherme Almeida, Leonardo Santana, Luciana Leite, Solange M. Sanches, Vladmir Cordeiro de Lima, Rafaela Pirolli, Rafael Manea, Felipe Kaneta, Jean Coutinho, Lucas Vian, Waires Zeviani, Marcio Reis, Luciana Landeiro, Clarissa Mathias, Geila Nunez, Tamara Santana, Monique Tavares. Clinical-pathological determinant factors to choose between four or six cycles of adjuvant chemotherapy with docetaxel/cyclophosphamide (TC) in a retrospective real-world cohort of HER2-negative breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-02-14.