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11530 Background: Survival after relapse in osteosarcoma (OST), Ewing Sarcoma (ES) and chondrosarcoma (CS) remains dismal. Recent reports suggest a role of tyrosine kinase inhibitors (TKI) including regorafenib (R) and cabozantinib (C). We conducted a retrospective multi-centre pan-Canadian study to assess real-word outcomes with these novel treatments in recurrent BT. Methods: After ethics approval, data from pts treated in 7 different institutions was extracted from the CanSaRCC (Canadian Sarcoma Research and Clinical Collaboration) Database. Pt characteristics, treatment and outcomes were analyzed. Response was assessed per RECIST 1.1. PFS, OS were estimated using Kaplan-Meier. TTP was defined as time from TKI start to progression. Results: From June 2018-Dec 2021, 44 pts received R or C and best response by histology are listed in Table, with an overall clinical benefit rate of 63.6%. Median time to best response was 2.3 mo (range 1 – 17). 15 pts (34.1%) required dose reduction; most common reasons were hand-foot syndrome (13.6%), mucositis (9.1%) and hypertension (9.1%). At median FU of 6.4 mo (range 1.6 – 29), 25 pts (56.8%) died, 19 (43.2%) were alive with disease (AWD). Median PFS was 4.1 mo (95%CI 2.9 – 5.7), for OST was 5.0 (N = 25, 95%CI 2.6 – 10.6), for ES was 4.1 (N = 10, 95%CI 2-5.9), and for CS 4.0 (N = 9, 1 Progressed). Median OS was 10.5 mo (95%CI 7 – 14). By univariate analysis, age, line of therapy, gender, location of primary, or R vs. C did not correlate with PFS. Conclusions: Consistent with previous published studies, our pan-country real-world analysis shows that TKI have meaningful activity in the setting of recurrent BT with acceptable toxicities. Inclusion in earlier lines of treatment and/or maintenance therapy could be questions for future research. [Table: see text]

9069 Background: ICIs have limited efficacy in EGFR+ NSCLC with ORR ~10% if PDL1 > 25% in ATLANTIC, yet ICIs are often used in later lines of therapy as pts and providers feel there may be little risk. The impacts of ICI in this setting are poorly understood. We describe our institutional experience of ICI use in EGFR+ NSCLC. Methods: MGH pts with advanced EGFR+ NSCLC treated with ICI (any line) were retrospectively reviewed for demographics, PDL1, treatment duration and patient outcomes. Disease flare was defined as hospital/hospice admission due to progression or death (Chaft CCR 2011) within 30d of ICI. Results: 40 pts with EGFR+ NSCLC (22 del19, 11 L858R, 5 ins20, 2 other) received ICI between 7/2012-12/2018. 13 were on a clinical trial. 4 had SCLC transformation. Median # of prior therapies = 3 (range, 0-8). Of 16 with PDL1 quantified, 8 had PDL1 > 25%. ICI regimens were: nivolumab (nivo; n = 16), pembrolizumab (pembro; 9), atezolizumab (atezo; 3), ipilimumab/nivo (7), carboplatin/pemetrexed (pem)/pembro (3), pem/pembro (1), paclitaxel/atezo (1). 18 pts stopped TKI ≤21d prior to ICI start. Median duration of treatment (DOT) was 25 days (range, 1-1482). DOT was > 1 yr for 2 pts (5%), treated with 1st-line nivo/erlotinib (erlo) and 3rd-line nivo. All 8 pts with PDL1 > 25% had DOT < 2 mos. Disease flare within 30d of ICI occurred in 16/40 (40%) overall, 8/18 (44%) who stopped TKI ≤21d of ICI start, and 14/26 (54%) who received ICI in 4thline or later. 8 pts had concurrent TKIs (4 erlo/nivo, 2 erlo/pembro, 1 erlo/atezo, 1 osimertinib (osi)/nivo); 3/8 discontinued ICI for toxicity (all 3 treated first-line). 5 pts received osi immediately post-ICI. There was no pneumonitis on osi post-ICI; 1 pt developed gr3 LFTs and gr4 hypoNa. Conclusions: In this real world cohort of EGFR+ NSCLC, clinical benefit from ICI (assessed by DOT) was rare, including pts with high PDL1. 5% had durable benefit (both pts received ICI in earlier lines of therapy). A previously underappreciated negative outcome of ICI is that admission to hospital, hospice or death within 30d of ICI occur in up to 54% pts. This may be related to disease flare or hyperprogression and suggests that use of ICI in heavily pretreated EGFR+ NSCLC may negatively impact outcomes at end-of-life and should be used with caution.

8573Background: 5-10% of EGFR-mutant ACs undergo SCLC/neuroendocrine transformation (SCLC-T) but the clinical course of such pts is poorly characterized. Methods: We identified 50 pts with EGFR-mut...

e21231Background: Osimertinib (osi) is a potent, CNS-penetrant 3rd-generation EGFR TKI. Though older TKIs did not add benefit to chemo (IMPRESS, Soria et al 2015), combining osi with chemo to prolo...