Background: Obesity is a risk factor for many breast cancer (BC) subtypes & is associated w/ inferior BC outcomes. Here, we investigate the effect of a NCCN based intervention on weight loss (WL) in BC pts. Methods: Prospective study using WL guidelines adapted from NCCN Survivorship (V. 2.2017). Data collected: demographics, clinical, cardiovascular risk factors (CVD), weight, height, body fat%. Stats: 1 sample T-Test w/ 2 tail p-value & 95% CI used to calculate change in weight from baseline to 3 & 6 months (mo) using hypothetical mean of 0. Inclusions: Female BC pts, stage 0-III, OW (BMI > 25mg/m2) or OB (BMI > 30kg/m2). Exclusions: No BC, stage IV, not OW/OB, lost to follow up (f/u), non-compliance, death, or recurrent disease. Intervention: BMI assessed at baseline at initial visit where pt received 20 minute OB counseling by oncologist (ONC). Pts include NEW pts (treatment & surgery naïve) & F/U pts (pts finished definitive treatment in survivorship). ONC counseling included pt education on OB & cancer outcomes & CVD risk. Initially, pts referred to physical therapy (PT) for exercise program & dietician (DT) for nutrition counseling. Pts visit PT & DT q 3 mo. ONC counseling provided periodically during scheduled visits. Results: 70 pts enrolled 10/26/2017 – 10/8/2018. Median pt age = 56 yrs (37-87). Menopausal status: 25/70 (36%) pre menopause vs. 45/70 (64%) post menopause. Race: 29/70 Caucasian (41%), 41/70 (59%) African American, 0/70 (0%) other. Ethnicity: 2/70 (3%) Latin vs. 68/70 (97%) non-Latin. Avg. BMI = 34 kg/m2 (26-54). Avg. weight = 90 kg (61-143). Stage: 0 = 7/70 (10%) , I = 26/70 (37%), II = 21/70 (30%), III = 16/70 (23%). Receptors: 12/70 (17%) triple negative, 13/70 (19%) Her-2+, 49/70 (70%) ER/PR+. CVD risk factors & body fat% shown separately. Mean WL for the 70 pts (NEW + F/U, N = 70) = -0.7 kg @ 3 mo. (p = 0.08), 95%CI (-1.510- +0.101); mean WL = -0.7 kg @ 6 mo. (p = 0.16), 95%CI (-1.703-+0.295). Mean WL for NEW pts, (N = 52) lost -0.9 kg @ 3 mo. (p = 0.0467), 95%CI (-1.809- -0.014). New pts lost -0.7 kg @ 6 mo. (p = 0.21), 95% CI (-1.868 - +0.440). Conclusions: Implementation of the NCCN guidelines + ONC counseling as part of a WL program mitigates weight gain @ 3 & 6 mo in all OW & OB BC pts & induced significant weight loss in NEW pts @ 3 mo.