Abstract Background NSABP B-36 compares 6 cycles of FEC-100 with 4 cycles of standard AC in pts with node-negative breast cancer. As reported separately, no significant differences between the two treatment arms were observed in the primary endpoint of disease-free survival or in the secondary endpoints of overall survival, recurrence-free, or distant recurrence-free intervals. Greater toxicity was reported in pts who received FEC compared to AC. We present here the results of the QOL and MH studies obtained prospectively in conjunction with the treatment study. We hypothesized that pts on FEC would experience greater treatment toxicity in the first 12 months of the study, and would have greater rates of amenorrhea at 18 months compared to pts on AC. Methods Among the 1,357 pts enrolled in the QOL study, 1,332 (675 AC, 657 FEC) submitted the baseline form and had QOL follow-up (fup) information. Pts completed: 1) the FACT-B instrument; 2) a symptom checklist; and 3) the SF-36 Vitality Scale, all at baseline, day 1 of cycle 4, and at 6, 12, 18, 24, 30, and 36 months after random assignment. FACT-B Trial Outcome Index (TOI), symptom severity, and vitality scores were compared between the two treatment arms using a mixed model for repeated measures analysis with adjustment for the baseline scores, type of surgery, and hormone receptor status, examining the first 12 months and the later time points separately. Menstrual status was collected at baseline for all enrolled pts, with subsequent assessments on day 1 of cycle 4, and at 6, 12, 18, 24, 30, and 36 months for pts with menstrual bleeding within 12 months prior to random assignment and not having had a hysterectomy and/or bilateral oophorectomy (1, 096 pts). Post-chemotherapy amenorrhea was defined as the lack of menstrual periods during the 12 months preceding the 18-month fup evaluation. Data from 921 pts (475 AC, 446 FEC) were available for analysis. Logistic regression, adjusted for type of surgery and hormone receptor status, was used to test for association of amenorrhea status and treatment. Results Both TOI and vitality scores were worse for pts on FEC compared to those on AC at 6 months (p<0.01) with no significant difference at 12 months and beyond. No significant differences in symptom severity between the two treatment arms were observed. The rates of post-chemotherapy amenorrhea were significantly different between FEC and AC (66.8% vs. 58.7%, p=0.01) with positive hormone receptor status as an independent risk factor (p=0.03). Conclusions Women receiving FEC had diminished QOL at 6 months after random assignment, but no difference at 12 months or later. Premenopausal women receiving FEC experienced a higher rate of post-chemotherapy amenorrhea than women receiving AC. Support NCI grants U10-CA-12027, -37377, -69974, -69651 and -44066-26, and Pharmacia & Upjohn Company, a subsidiary of Pfizer, Inc. Citation Format: Patricia A Ganz, John W Wilson, Hanna Bandos, André Robidoux, Alexander HG Paterson, Johnathan Polikoff, Luis Baez-Diaz, Adam M Brufsky, Louis Fehrenbacher, Aroop Mangalik, Patrick J Ward, Louise Provencher, John T Hamm, Philip J Stella, Robert L Carolla, Richard G Margolese, Henry R Shibata, Edith A Perez, Norman Wolmark. Impact of treatment on quality of life (QOL) and menstrual history (MH) in the NSABP B-36: A randomized phase III trial comparing six cycles of 5-fluorouracil (5-FU), epirubicin, and cyclophosphamide (FEC) to four cycles of adriamycin and cyclophosphamide [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-12-01.