Abstract Introduction: Breast cancer is the most common among women worldwide. Approximately 67% of women with breast cancer are hormone receptor (RH) positive, so adjuvant endocrine therapy is often used. However, the impact of aromatase inhibitors on maintaining bone mineral density is discussed. Objective: Verify whether Vitamin D and Calcium supplementation impacted the progression to osteopenia and osteoporosis in the evaluated groups. Methodology: Comparative prospective cohort study with 140 women, divided into 2 groups; IAG (RH+ in treatment with aromatase inhibitors) and CG (triple- or HER-2 positive in another type of treatment). After approval of the project by the ethics committee, the mineral density of the lumbar spine, femoral neck and total femur (T-score) was analyzed by imaging before, after 6 months and 5 years of treatment. Blood tests to measure serum calcium, ionic calcium, vitamin D and parathyroid hormone (PTH) were performed before and after 5 years, where results less than 30ng/mL vitamin D were treated with 7,000UI per day (dose of attack), for eight weeks followed by daily maintenance of 1000UI, in the presence of Osteopenia they received calcium and Osteoporosis received zoledtobic acid (4mg), 6/6 months. Data were initially analyzed by the KS test to determine the normality of the sample, later by the Anova Test, considering p≤0,05. Results: Regarding vitamin D, before treatment, 45 (64%) and 56 (71%); after 5 years, 12 (17%) and 11 (16%) were respectively insufficient in the IAG and CG. In the progression to osteopenia, the changes were statistically significant in the femoral neck (4-12%,12-17%/9-12%,11-15%) and in the femur (7-10%,18-25%/6-8%,17-24%) after 6 months and 5 years, respectively in the IAG and CG. In the lumbar spine, despite showing progression to osteoporosis, it was not statistically significant, as well as in the comparison of groups. Both, IAG and the CG showed statistically significant loss of bone mass in the femur and femur neck when compared before treatment with 6 months and 5 years (p≤0,05). In the spine, the statistically significant loss occurred comparing before treatment with 6 months only in the IAG (p=0,05). When comparing the groups with each other, we found no statistically significant diferences. Conclusion: Vitamin D and calcium supplementation appears to have generated a protective factor in bone loss in both groups. Table 1.T-score values at the evaluated times (n=140).Aromatase Inhibitors GroupFEMORAL NECKFEMURLUMBAR SPINEBefore6M5YBefore6M5YBefore6M5YNormal383426514433384238Osteopenia323644192637322226Osteoporosis000000066p-value0,002*0,000*0,03*0,01*0,10,2Control GrroupNormal393028524635503939Osteopenia31404218243592624Osteoporosis0000001157p-value0,05*0,006*0,05*0,002*0,40,2M: Months; Y: Years. Table 2.Bone mineral density at the evaluated times (n=140).Aromatase Inhibitors GroupFEMORAL NECKBefore6M5YLoss 6MLoss 5YMean±SD0,95±0,130,89±0,160,85±0,14-5,75±13,51-9,41±13,79p-value0,019*0,0003*0,070,05*FEMURMean±SD1,01±0,180,96±0,190,92±0,17-4,25±14,67-7,87±16,05p-value0,05*0,001*0,090,08LUMBAR SPINEMean±SD1,13±0,161,11±0,171,07±0,22-1,5±6,96-4,57±15,45p-value0,270,05*0,140,06Control GrroupFEMORAL NECKBefore6M5YGain 6MLoss 5YMean±SD0,94±0,130,89±0,150,85±0,15-4,36±21,80-8,10±20,26p-value0,01*0,0001*0,10,14FEMURBefore6M5YLoss 6MLoss 5YMean±SD1,0±0,190,94±0,170,92±0,18-2,03±28,92-5,31±21,94p-value0,02*0,007*0,260,22LUMBAR SPINEMean±SD1,1±0,191,11±0,161,07±0,223,77±25,83-0,85±24,89p-value0,410,150,10,14M: Months; Y: Years; SD: Standard Deviation Citation Format: Marcelo Antonini, Gisela RosaFranco Salerno, Natalia DanielaKovalinski Vieira, Mariana Soares Cardoso, Matheus de Paula Solino, Raissa Naiarade Barros Vasconcelos, Lais de Albuquerque Vasconcelos, Odair Ferraro, Andre Mattar, Reginaldo GuedesCoelho Lopes, Juliana Monte Real. Evaluation of the impact Vitamin D and Calcium supplementation on bone mineral density in breast cancer patients using or not taking Aromatase Inhibitors: 5-year follow-up [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-13-04.