Bone Mineral Density (Bmd) In Participants (Pts) Of Trial Big 1-98 Comparing Adjuvant Letrozole (L) Versus Tamoxifen (T) Or Their Sequence

516 Background: BIG 1-98 compared adjuvant hormonal therapies in over 8,000 postmenopausal pts with operable, ER-positive breast cancer: 5 years (yrs) of T; 5 yrs of L; sequence of 2 yrs T followed by 3 yrs L (TL); 2 yrs L followed by 3 yrs T (LT). During therapy fractures were more frequent in L (9.8%) and TL (9.4%) compared with T (7.3%) and LT (7.5%); the effect of the regimens on BMD is unknown. Methods: BMD was measured annually by dual energy X-ray absorption in 458 patients enrolled after 3 (n=152), 4 (n=194), and 5 (n=71) yrs from randomization and 1 yr off-treatment. Spine and femur T-scores were analyzed by mixed linear models using time from randomization, treatment allocation, time from randomization by treatment interaction, age, BMI, and prior HRT use as covariates. Results: Pts and tumor characteristics in the substudy did not differ significantly from the main study and among treatment arms. T-score estimates (standard errors) based on the mixed linear model are summarized in the table. BMD in T was superior to the other arms at all time points in spine and femur. Pts on T had better overall BMD than pts on L (overall difference in T-score: Spine=0.42, p=0.06; Femur=0.43, p=0.0007). Pts on LT had better overall BMD than pts always on L (overall difference in T-score: Spine=0.07, p=0.72; Femur=0.22, p=0.06). Notably, in pts on LT, BMD improved with T therapy. One year after treatment completion, the proportion of women with osteoporosis (T-score< 2.5) was 9% on T, 21% on L, 22% on TL and 18% on LT. Conclusions: As expected, adjuvant L therapy causes loss of BMD compared with T in postmenopausal pts. However, the sequence L followed by T appears to preserve BMD while retaining the efficacy of upfront L. Yrs after randomization Treatment arm T L TL LT Spine (L2-4) 3 -0.54 (0.19) -1.09 (0.16) -1.20 (0.16) -1.07 (0.16) 4 -0.69 (0.18) -1.06 (0.15) -1.36 (0.16) -0.98 (0.15) 5 -0.62 (0.18) -1.08 (0.15) -1.36 (0.16) -0.90 (0.15) 6 -0.73 (0.19) -1.00 (0.15) -1.22 (0.16) -0.99 (0.15) Femur 3 -0.86 (0.11) -1.28 (0.09) -1.33 (0.10) -1.20 (0.10) 4 -0.72 (0.11) -1.30 (0.09) -1.44 (0.09) -1.03 (0.08) 5 -0.90 (0.11) -1.29 (0.08) -1.39 (0.09) -0.97 (0.08) 6 -0.89 (0.12) -1.25 (0.08) -1.33 (0.09) -1.05 (0.08)