Abstract P1-13-11: Optimal omission of anthracycline in adjuvant chemotherapy of HER2 positive breast cancer

Abstract [Background]In adjuvant settings of HER2 positive cancer, trastuzumab has been shown to be effective in combination with anthracycline- based chemotherapy followed by taxane-based chemotherapy. However, the role of anthracyclines for the treatment of breast cancer has remained in controversy,due to the increased risk of cardiotoxicity and secondary carcinogenesis. Recently, additional anthracycline-free treatment regimens have also been reported. In a single-arm multicenter trial of 406 patients treated with paclitaxel plus trastuzumab for <3cm, lymph node negative, HER2 positive breast cancer,Tolaney et al reported a 98.7% rate of survival free from invasive disease at 3 years of follow-up (NEJM 2015). NCCN guideline 2018 suggests paclitaxel plus trastuzumab to be considered for patients with low-risk T1, N0, M0, HER2 positive breast cancer. However, there is a lack of definitive evidence for anthracycline-free regimens in adjuvant chemotherapy of HER2 positive cancer. We performed a single-center retrospective cohort study to assess the characteristics of patients we can safely omit anthracyclines in the adjuvant settings for HER2 positive breast cancer. [Patients and methods]238 women werediagnosedwith HER2 positive breast cancer and treated with neoadjuvant and/or adjuvant chemotherapy between January 1,2008 and December 31,2015 at Keio University Hospital.They were divided in two cohorts: an “anthracycline” cohort of 112 anthracycline-treated women and a “no anthracycline” cohort of 126 anthracycline-untreated women. [Results]Three years disease free survival(DFS) was 91.3% (95% CI,84.0%–95.4%)and 93.1% (95% CI,86.1%–96.7%)in the no anthracycline and anthracycline cohorts,respectively. There were no significant differences between the two cohorts (P=0.692). Among the cT1N0 subset, no significant differences were observed between two cohorts in 3 years DFS (P=0.612). However, the patient characteristics of the cT2 subset were not balanced enough to compare the two cohorts. Of the 238 patients, 122 received neoadjuvant chemotherapy and 36 (29.5%) of them achieved pathological complete response (pCR). Among the pCR group, only one patient in each cohort had recurrence. [Discussion]We suggest that we can safely omit anthracyclines in cT1N0 HER2 positive breast cancer patients and also in patients who achieved pCR by neoadjuvant chemotherapy. However, we need a larger number of cases to assess the possibility of omission in cT2 HER2 positive breast cancer. Current clinical trials indicate the addition of pertuzumab to trastuzumab for neoadjuvant and adjuvant chemotherapy in HER2 positive breast cancer leads to a good pCR rate and increase the efficacy of anti HER2 block therapy. We expect that the additional use of pertuzumab with trastuzumab will widen the possibility of anthracycline-free adjuvant chemotherapy in HER2 positive cancer. Citation Format: Watanuki R, Hayashida T, Yuko K, Kikuchi M, Nakashoji A, Yokoe T, Toyota T, Seki T, Takahashi M, Kitagawa Y. Optimal omission of anthracycline in adjuvant chemotherapy of HER2 positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-13-11.