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RMND1 has been identified as a mitochondriopathy-associated gene less than 12 years ago. The most common phenotype related to this gene is an early onset, severe form of encephalomyopathy that leads to death in a medium time of three years after birth. However, milder and later onset presentations have been reported in some individuals, including two in whom the mitochondriopathy was identified at ~ 40 years of age, and the early onset presentations have been the object of no reports in those who survived beyond age 10. It is thus unclear how lethal RMND1-related conditions really are. We herein describe the oldest case to have been identified hitherto with this condition, i.e., that of a white female who was 61 at the time of diagnosis but was still active in her everyday life. The gene defect identified was nonetheless associated with many manifestations including ovarian insufficiency and sensorineural hearing loss (two features of what is currently designated as Perrault syndrome) as well as chronic renal failure, asymptomatic myopathy, leukopenia and a few others. In our opinion, this case is of great translational interest for at least three reasons. First, it hints towards the possibility of near-normal life expectancies in some if not many individuals with RMND1 insufficiency. Second, it underlines the wide clinical spectrum associated with this gene. Third, it brings us to question the use of eponyms and syndromic features to identify the true etiology of multisystemic phenotypes.

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The PACIFIC trial demonstrated that durvalumab therapy following chemoradiation (CRT) was associated with improved overall survival (OS) in patients with stage III non-small cell lung cancer (NSCLC). It is unclear whether the results obtained as part of randomised controlled trials are a reflection of real-world (RW) data. Several questions remain unanswered with regard to RW durvalumab use, such as optimal time to durvalumab initiation, incidence of pneumonitis and response in PD-L1 subgroups.In this multicentre retrospective analysis, 147 patients with stage III NSCLC treated with CRT followed by durvalumab were compared with a historical cohort of 121 patients treated with CRT alone. Survival curves were estimated using the Kaplan-Meier method and compared with the log-rank test in univariate analysis. Multivariate analysis was performed to evaluate the effect of standard prognostic factors for durvalumab use.Median OS was not reached in the durvalumab group, compared with 26.9 months in the historical group (hazard ratio [HR]: 0.56, 95% confidence interval [CI]: 0.37-0.85, p = 0.001). In the durvalumab group, our data suggest improved 12-month OS in patients with PD-L1 expression ≥50% (100% vs 86%, HR: 0.25, 95% CI: 0.11-0.58, p = 0.007). There was no difference in OS between patients with a PD-L1 expression of 1-49% and patients with PD-L1 expression1%. Delay in durvalumab initiation beyond 42 days did not impact OS. Incidence of pneumonitis was similar in the durvalumab and historical groups. In the durvalumab group, patients who experienced any-grade pneumonitis had a lower 12-month OS than patients without pneumonitis (85% vs 95%, respectively; HR: 3.3, 95% CI: 1.2-9.0, p = 0.006).This multicentre analysis suggests that PD-L1 expression ≥50% was associated with favourable OS in patients with stage III NSCLC treated with durvalumab after CRT, whereas the presence of pneumonitis represented a negative prognostic factor.

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]

We present a cohort of 41 patients with osimertinib resistance biopsies, including 2 with an acquired CCDC6–RET fusion. Although RET fusions have been identified in resistant EGFR-mutant non–small cell lung cancer (NSCLC), their role in acquired resistance to EGFR inhibitors is not well described. To assess the biological implications of RET fusions in an EGFR-mutant cancer, we expressed CCDC6–RET in PC9 (EGFR del19) and MGH134 (EGFR L858R/T790M) cells and found that CCDC6–RET was sufficient to confer resistance to EGFR tyrosine kinase inhibitors (TKI). The selective RET inhibitors BLU-667 and cabozantinib resensitized CCDC6–RET-expressing cells to EGFR inhibition. Finally, we treated 2 patients with EGFR-mutant NSCLC and RET-mediated resistance with osimertinib and BLU-667. The combination was well tolerated and led to rapid radiographic response in both patients. This study provides proof of concept that RET fusions can mediate acquired resistance to EGFR TKIs and that combined EGFR and RET inhibition with osimertinib/BLU-667 may be a well-tolerated and effective treatment strategy for such patients. Significance: The role of RET fusions in resistant EGFR-mutant cancers is unknown. We report that RET fusions mediate resistance to EGFR inhibitors and demonstrate that this bypass track can be effectively targeted with a selective RET inhibitor (BLU-667) in the clinic. This article is highlighted in the In This Issue feature, p. 1494

We present a cohort of 41 patients with osimertinib resistance biopsies, including two with an acquired CCDC6-RET fusion. While RET fusions have been identified in resistant EGFR-mutant NSCLC, their role in acquired resistance to EGFR inhibitors is not well described. To assess the biological implications of RET fusions in an EGFR-mutant cancer, we expressed CCDC6-RET in PC9 (EGFR del19) and MGH134 (EGFR L858R/T790M) cells and found that CCDC6-RET was sufficient to confer resistance to EGFR-TKIs. The selective RET inhibitors BLU-667 or cabozantinib resensitized CCDC6-RET-expressing cells to EGFR inhibition. Finally, we treated two patients with EGFR-mutant NSCLC and RET-mediated resistance with osimertinib and BLU-667. The combination was well-tolerated and led to rapid radiographic response in both patients. This study provides proof-of-concept that RET fusions can mediate acquired resistance to EGFR TKIs and that combined EGFR and RET inhibition with osimertinib/BLU-667 may be a well-tolerated and effective treatment strategy for such patients.

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...