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3063 Background: Several studies showed that high baseline tumor size (BTS) is associated with worse outcomes in cancer patients treated with immunotherapy (IO). However, the prognostic impact of BTS for patients receiving targeted therapies (TT) remains uncertain. Methods: We collected clinical data for patients with solid tumors consecutively treated within early phase trials at our institution from 01/2014 to 04/2021. Treatments were categorized as IO-based (if any IO-agent was included) or TT-based (biomarker-matched or not). BTS was calculated as the sum of RECIST 1.1 baseline target lesions. Progression-free survival (PFS), overall survival (OS) and objective-response rate (ORR) were compared between patients with high BTS (> median) and low BTS (≤median). Results: 444 patients were eligible for the analysis (220 IO, 151 TT biomarker-matched, 73 TT biomarker-unmatched). Median age was 56 years (interquartile range, IQR 48-64) and median BTS was 69 mm (IQR 40-100). Most represented tumor types were breast (49%), lung (9%), melanoma (5%) stomach, colorectal, head and neck and ovarian (4% each). Patients with low BTS were more often female (p < 0.001), had a better performance status (PS, p = 0.008), lower LDH (p < 0.001), lower neutrophile/lymphocyte ratio (NLR, p < 0.001) and higher albumin (p = 0.003). OS was significantly longer for patients with low BTS (16.6 vs 8.2 months, p < 0.001), including when restricting at those receiving IO (12 vs 7.5 months, p = 0.005). Among patients receiving TT, those with lower BTS experienced longer PFS (4.7 vs 3.1 months, p = 0.002) and OS (20.5 vs 9.9 months, p < 0.001) as compared with those with high BTS. However, BTS was only prognostic among patients receiving biomarker-matched TT, with improved PFS (6.2 vs 3.3 months, p < 0.001) and OS (21.2 vs 6.7 months, p < 0.001) in the low-BTS subgroup, despite a similar ORR (28% vs 22%, p = 0.57). BTS was instead not prognostic among patients receiving unmatched TT, with similar PFS (3.7 vs 4.4 months, p = 0.30), OS (19.3 vs 11.8 months, p = 0.20) and ORR (33% vs 28%, p = 0.78) in the two BTS groups. Multivariate analysis confirmed that BTS was independently associated with PFS (p = 0.03) and OS (p < 0.001) but not with ORR (p = 0.11), regardless of tumor site, treatment category, PS, NLR, sites of metastases and number of prior lines. Conclusions: Patients receiving biomarker-matched TT experience longer PFS and OS if having a lower BTS, whereas response rate is not affected by this variable. This difference may reflect the faster emergence of molecular mechanisms of resistance among patients with higher baseline burden. Lower BTS is also confirmed to be associated with longer survival among patients receiving experimental IO. BTS has instead no prognostic value among patients receiving unmatched TT.

9541 Background: Immune-checkpoint inhibitors (ICI) and targeted-therapies (TT) have become standard options for BRAF -V600 metastatic melanoma (B-mut MM) patients. However, still more than 50% of those patients do not respond or relapse to these current strategies. Preclinical and translational data suggest that ICI plus TT may improve treatment outcomes in patients with B-mut MM, but with conflicting results in the clinical setting. Methods: We performed a systematic review and meta-analysis of randomized phase II-III studies published until January 2022 comparing first-line ICI+TT vs TT alone in B-mut MM. We obtained summary estimates through random-effects models. Overall survival (OS) and progression-free survival (PFS) were the main outcomes retrieved but we look also at difference in responses and adverse events. Results: We summarized data from 3 independent trials and we showed a significant advantage in terms of PFS and OS for the experimental arms in B-mut MM patients treated with ICI+TT rather than TT alone. The summary estimate indicates a significant 23% decrease in risk of progression (SHR = 0.77, 95%CI: 0.66-0.89, with no between-study heterogeneity I2= 0%) and a significant 21% reduction in risk of death (SHR = 0.79, 95%CI: 0.66-0.96, with no heterogeneity I2= 0%). However, no difference was shown (p-value = 0.56) between arms in terms of summary Objective Response Rate (ORR) estimates (Summary ORR doublet = 65.4% [61.5%; 69.2%] and Summary ORR triplet = 67% [63%; 70.9%], respectively). From the subgroup analysis on PFS risk estimates, no significant differences were observed in summary HRs by age ( < 65 vs ≥65 years, p-value = 0.11), sex (female vs male, p-value = 0.58), ECOG PS (0 vs 1, p-value = 0.36), LDH levels (lower vs upper, p-value = 0.59) and PDL1 status (positive vs negative, p-value = 0.89). Significant differences were found in frequencies of grade 3 or more adverse events with higher number of events occurring in B-mut MM vs TT alone (Summary Odd Ratio = 2.01, 95%CI: 1.16-3.47, I2= 74%), whereas no significant differences were found in terms of any adverse event between arms (SOR = 1.83, 95%CI: 0.70-4.78, I2= 0%). Conclusions: This study supports and extend the discussion on first-line available combinations to be offered to B-mut MM patients. Combining ICI with TT demonstrated an effective advantage on both PFS and OS, although augmenting toxicities. Further biomarker-driven investigation may identify patient subpopulations who could benefit from ICI+TT combinations in order to expand their window of therapeutic opportunities.