Body composition modulations during cyclic fasting-mimicking diet in patients with advanced solid cancers.

3156 Background: Fasting-mimicking diets (FMD) can induce favorable immune-metabolic changes in humans and preclinical data suggest potential antitumor activity. Cyclic FMD impact on muscle mass and adiposity in patients (pts) is unclear. Here we evaluate body composition changes in pts with advanced solid cancers undergoing FMD in the context of a phase Ib trial (NCT03340935). Methods: NCT03340935 study evaluated safety and biological effects of a cyclic FMD consisting of a 5-day, calorie-restricted, plant-based diet repeated every 21-28 days for a maximum of 8 cycles, conducted in oncologic patients receiving concomitant therapies. Here we included pts with advanced solid cancers and Computed Tomography (CT) exams at baseline (BL), FMD end and disease progression (PD). Body composition parameters, i.e. Skeletal Muscle Index (SMI) and Visceral (VAT), Subcutaneous (SAT), Intermuscular (IMAT) Adipose Tissues, were assessed via axial CT scan at 3 rd lumbar vertebra using SliceOmatic software. Pts with advanced triple negative breast cancer (TNBC) receiving chemotherapy (ChT) without FMD, having CT scans at BL and PD, were selected as control cohort. Wilcoxon tests were used for comparisons. Results: In the FMD cohort (n=36), 61% had BC, 39% had TNBC, 78% received ChT; median age was 54 (IQR 51-65), median completed FMD cycles was 5 (IQR 3-8), median time from FMD end to PD was 3.5 months (IQR 1.0-16.0); 8 pts met criteria for sarcopenia (SMI &lt;38.5 cm 2 /m 2 ) at BL, 6 of whom had TNBC. In the control TNBC cohort (n=17), median age was 54 (IQR 42-68), 6 pts were sarcopenic at BL. In the FMD cohort, between BL and FMD end there was a significant reduction of VAT, SAT and SMI, but no change in IMAT; between BL and PD only SMI was significantly decreased (Table). At FMD end and PD, 12 pts were sarcopenic in the FMD cohort, 7 having TNBC. In the control TNBC cohort (n=17), IMAT was significantly increased between BL and PD, with no changes in other parameters (Table); 8 pts were sarcopenic at PD. Conclusions: In advanced cancers pts, cyclic FMD reduces adiposity as well as muscle mass. Tumor/therapy-related factors contribute to sarcopenia in advanced cancer pts, thus future trials involving FMD intervention should detect pts at risk and include supportive measures to preserve muscle mass. Support: Italian Association for Cancer Research (AIRC): AIRC-Bonadonna fellowship (C Sposetti), AIRC fellowship (F Ligorio), AIRC IG 2024 ID 30499 (PI: C Vernieri); Giuliani Foundation. Clinical trial information: NCT03340935 . Visceral Adipose Tissue change - % median p value Subcutaneous Adipose Tissue change - % median p value Intermuscular Adipose Tissue change - % median p value Skeletal Muscle Index change - % median p value FMD end vs BL FMD cohort, n=36 -12.4 0.002 -11.9 &lt;0.001 +0.9 0.55 -4.2 0.014 PD vs BL FMD cohort, n=36 -6.2 0.25 -5.5 0.083 +1.2 0.5 -5.1 &lt;0.001 TNBC subset, n=14 -3.2 0.24 -5.0 0.042 +0.2 0.9 -4.7</