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Introduction: Mechanisms of resistance to EGFR exon 20 insertion mutation active inhibitors have not been extensively studied in either robust preclinical models or patient-derived rebiopsy specimens. We sought to characterize on-target resistance mutations identified in EGFR exon 20 insertion-mutated lung cancers treated with mobocertinib or poziotinib and evaluate whether these mutations would or would not have cross-resistance to next-generation inhibitors zipalertinib, furmonertinib, and sunvozertinib. Methods: We identified mechanisms of resistance to EGFR exon 20 insertion mutation active inhibitors and then used preclinical models of EGFR exon 20 insertion mutations (A767_V769dupASV, D770_N771insSVD, V773_C774insH) plus common EGFR mutants to probe inhibitors in the absence/presence of EGFR-T790M or EGFR-C797S. Results: Mobocertinib had a favorable therapeutic window in relation to EGFR wild type for EGFR exon 20 insertion mutants, but the addition of EGFR-T790M or EGFR-C797S negated the observed window. Zipalertinib had a favorable therapeutic window for cells driven by EGFR-A767_V769dupASV or EGFR-D770_N771insSVD in the presence or absence of EGFR-T790M. Furmonertinib and sunvozertinib had the most favorable therapeutic windows in the presence or absence of EGFR-T790M in all cells tested. EGFR-C797S in cis to all EGFR mutations evaluated generated dependent cells that were resistant to the covalent EGFR tyrosine kinase inhibitors mobocertinib, zipalertinib, furmonertinib, sunvozertinib, poziotinib, and osimertinib. Conclusions: This report highlights that poziotinib and mobocertinib are susceptible to on-target resistance mediated by EGFR-T790M or -C797S in the background of the most prevalent EGFR exon 20 insertion mutations. Furmonertinib, sunvozertinib, and to a less extent zipalertinib can overcome EGFR-T790M compound mutants, whereas EGFR-C797S leads to covalent inhibitor cross-resistance—robust data that support the limitations of mobocertinib and should further spawn the development of next-generation covalent and reversible EGFR exon 20 insertion mutation active inhibitors with favorable therapeutic windows that are less vulnerable to on-target resistance.

ALK internal deletions of nonkinase domain exons occur in 0.01% of lung cancers with ALK genomic aberrations. We report a lung adenocarcinoma with a previously undescribed somatic ALK deletion of exons 2 to 19 with dramatic and sustained (>23 mo) response to alectinib. Our and other reported cases with ALK nonkinase domain deletions (between introns and exons 1–19) can display positive results in nonsequencing-based lung cancer diagnostic tests (such as immunohistochemistry) used to screen for more common ALK rearrangements. This case report emphasizes that “ALK-driven” lung cancers should be expanded to encompass those harboring not only ALK rearrangements with other genes but also ALK nonkinase domain deletions.

A 34-year-old woman presenting with abdominal pain, chest pressure, weight loss, and tachycardia was found to have an 11.4-cm anterior mediastinal mass associated with intrathoracic lymphadenopathy on chest computed tomography (Fig. 1A). Core needle biopsy was concerning for a type B1 thymoma.During this patient’s initial workup, she was found to have both clinical and laboratory evidence of Graves’ thyroiditis, raising diagnostic suspicion for thymic hyperplasia rather than thymoma. The case discussed here highlights the unique challenges that arise in the evaluation and management of thymic masses and serves as a prudent reminder that both benign and malignant disorders may present with mass-like changes.

Introduction: This multicenter review evaluated the efficacy and safety of osimertinib dose escalation for central nervous system (CNS) progression developing on osimertinib 80 mg in EGFR-mutant NSCLC. Methods: Retrospective review identified 105 patients from eight institutions with advanced EGFR-mutant NSCLC treated with osimertinib 160 mg daily between October 2013 and January 2020. Radiographic responses were clinically assessed, and Kaplan-Meier analyses were used. We defined CNS disease control as the interval from osimertinib 160 mg initiation to CNS progression or discontinuation of osimertinib 160 mg. Results: Among 105 patients treated with osimertinib 160 mg, 69 were escalated for CNS progression, including 24 treated with dose escalation alone (cohort A), 34 who received dose-escalated osimertinib plus concurrent chemotherapy and/or radiation (cohort B), and 11 who received osimertinib 160 mg without any prior 80 mg exposure. The median duration of CNS control was 3.8 months (95% confidence interval [CI], 1.7–5.8) in cohort A, 5.1 months (95% CI, 3.1–6.5) in cohort B, and 4.2 months (95% CI 1.6–not reached) in cohort C. Across all cohorts, the median duration of CNS control was 6.0 months (95% CI, 5.1–9.0) in isolated leptomeningeal progression (n = 27) and 3.3 months (95% CI, 1.0–3.1) among those with parenchymal-only metastases (n = 23). Patients on osimertinib 160 mg experienced no severe or unexpected side effects. Conclusion: Among patients with EGFR-mutant NSCLC experiencing CNS progression on osimertinib 80 mg daily, dose escalation to 160 mg provided modest benefit with CNS control lasting approximately 3 to 6 months and seemed more effective in patients with isolated leptomeningeal CNS progression.

Introduction: The development of immune-related adverse events (irAEs) has been associated with improved efficacy of immune checkpoint inhibitors in patients with urothelial cancer, melanoma, and NSCLC. Whether this association exists in patients with SCLC is currently unknown. Methods: We conducted a multicenter retrospective study to evaluate the relationship between irAEs and immunotherapy efficacy in SCLC. To account for the lead-time bias resulting from the time-dependent nature of irAEs, the development of irAEs was considered as a time-varying covariate in univariate and multivariate Cox proportional hazard models. Results: Of the 183 patients treated with immunotherapy, 73 (39.9%) experienced at least one irAE. A total of 42 patients (22.9%) had grade 1 to 2 irAEs, whereas 31 patients (16.9%) had grade 3 to 4 irAEs. The median time of onset to the first irAE was 24 days (interquartile range: 14–55). The baseline clinicopathologic features were well-balanced between patients with and without irAEs. At a median follow-up of 24 months (95% confidence interval [CI]: 17.0–31.6), the median progression-free survival was significantly longer in the irAE group than the non-irAE group (3.8 versus 1.3 mo, p < 0.0001). The median overall survival was also significantly longer among patients with irAEs than patients without irAEs (13.8 versus 2.9 mo, p < 0.0001). When analyzed as a time-varying covariate, the development of irAEs was associated with a significant improvement in progression-free survival (hazard ratio: 0.44 [95% CI: 0.29–0.66], p < 0.001) and overall survival (hazard ratio: 0.47 [95% CI: 0.32–0.71], p < 0.001) in multivariate models. Conclusions: The development of irAEs is associated with improved clinical outcomes for immunotherapy in patients with advanced SCLC.

Introduction: The EGFR-A763_Y764insFQEA is a unique exon 20 insertion mutation (∼5% to 6% of exon 20 insertions), which, at the structural and enzyme kinetic level, more closely resembles EGFR tyrosine kinase inhibitor (TKI)–sensitizing mutants, such as EGFR exon 19 indels and L858R. A limited number of preclinical models and clinical reports have studied the response of this mutant to EGFR TKIs. Methods: We used models of EGFR-A763_Y764insFQEA and more typical EGFR exon 20 insertion mutations to probe representative first- (gefitinib, erlotinib), second- (afatinib), third-generation (osimertinib), and in-development EGFR exon 20–specific (poziotinib, mobocertinib [TAK-788]) TKIs. We also compiled outcomes of EGFR-A763_Y764insFQEA-mutated lung cancers treated with EGFR TKIs. Results: Cells driven by EGFR-A763_Y764insFQEA were consistently sensitive to EGFR TKIs (as opposed to those driven by typical EGFR exon 20 insertions [A767_V769dupASV, D770_N771insSVD and H773_V774insH]), which were only inhibited by in-development EGFR TKIs at doses below those affecting wild-type EGFR. Most case instances (62.5% [95% confidence interval: 39%–86%], n = 16) with lung cancers harboring EGFR-A763_Y764insFQEA responded to clinically available EGFR TKIs (including osimertinib) and to in-development EGFR exon 20-specific TKIs (including mobocertinib) with prolonged periods of progression-free survival in some cases. Median overall survival for EGFR TKI–treated cases was 22 months (95% confidence interval: 16–25). Mechanisms of acquired TKI resistance of this mutant remain underreported, but do seem to align with those of common mutations. Conclusions: To our knowledge, this is the largest report to confirm that the EGFR-A763_Y764insFQEA mutation is sensitive to clinically available first-, second-, third-generation, and in-development EGFR TKIs.