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Mutations Analyzed

Purpose:The role of plasma-based tumor mutation burden (pTMB) in predicting response to pembrolizumab-based first-line standard-of-care therapy for metastatic non–small cell lung cancer (mNSCLC) has not been explored.Experimental Design:A 500-gene next-generation sequencing panel was used to assess pTMB. Sixty-six patients with newly diagnosed mNSCLC starting first-line pembrolizumab-based therapy, either alone or in combination with chemotherapy, were enrolled (Clinicaltrial.gov identifier: NCT03047616). Response was assessed using RECIST 1.1. Associations were made for patient characteristics, 6-month durable clinical benefit (DCB), progression-free survival (PFS), and overall survival (OS).Results:Of 66 patients, 52 (78.8%) were pTMB-evaluable. Median pTMB was 16.8 mutations per megabase (mut/Mb; range, 1.9–52.5) and was significantly higher for patients achieving DCB compared with no durable benefit (21.3 mut/Mb vs. 12.4 mut/Mb, P = 0.003). For patients with pTMB ≥ 16 mut/Mb, median PFS was 14.1 versus 4.7 months for patients with pTMB < 16 mut/Mb [HR, 0.30 (0.16–0.60); P < 0.001]. Median OS for patients with pTMB ≥ 16 was not reached versus 8.8 months for patients with pTMB < 16 mut/Mb [HR, 0.48 (0.22–1.03); P = 0.061]. Mutations in ERBB2 exon 20, STK11, KEAP1, or PTEN were more common in patients with no DCB. A combination of pTMB ≥ 16 and absence of negative predictor mutations was associated with PFS [HR, 0.24 (0.11–0.49); P < 0.001] and OS [HR, 0.31 (0.13–0.74); P = 0.009].Conclusions:pTMB ≥ 16 mut/Mb is associated with improved PFS after first-line standard-of-care pembrolizumab-based therapy in mNSCLC. STK11/KEAP1/PTEN and ERBB2 mutations may help identify pTMB-high patients unlikely to respond. These results should be validated in larger prospective studies.

pTMBand PD-L1 expression levels.

Development and validation of a plasma-based panel for mutation detection and assessment of TMB.

ImportanceDiffuse malignant peritoneal mesothelioma (DMPM) represents a rare and clinically distinct entity among malignant mesotheliomas. Pembrolizumab has activity in diffuse pleural mesothelioma but limited data are available for DMPM; thus, DMPM-specific outcome data are needed.ObjectiveTo evaluate outcomes after the initiation of pembrolizumab monotherapy in the treatment of adults with DMPM.Design, Setting, and ParticipantsThis retrospective cohort study was conducted in 2 tertiary care academic cancer centers (University of Pennsylvania Hospital Abramson Cancer Center and Memorial Sloan Kettering Cancer Center). All patients with DMPM treated between January 1, 2015, and September 1, 2019, were retrospectively identified and followed until January 1, 2021. Statistical analysis was performed between September 2021 and February 2022.ExposuresPembrolizumab (200 mg or 2 mg/kg every 21 days).Main Outcomes and MeasuresMedian progression-free survival (PFS) and median overall survival (OS) were assessed using Kaplan-Meier estimates. The best overall response was determined using RECIST (Response Evaluation Criteria in Solid Tumors) criteria, version 1.1. The association of disease characteristics with partial response was evaluated using the Fisher exact test.ResultsThis study included 24 patients with DMPM who received pembrolizumab monotherapy. Patients had a median age of 62 years (IQR, 52.4-70.6 years); 14 (58.3%) were women, 18 (75.0%) had epithelioid histology, and most (19 [79.2%]) were White. A total of 23 patients (95.8%) received systemic chemotherapy prior to pembrolizumab, and the median number of lines of prior therapy was 2 (range, 0-6 lines). Of the 17 patients who underwent programmed death ligand 1 (PD-L1) testing, 6 (35.3%) had positive tumor PD-L1 expression (range, 1.0%-80.0%). Of the 19 evaluable patients, 4 (21.0%) had a partial response (overall response rate, 21.1% [95% CI, 6.1%-46.6%]), 10 (52.6%) had stable disease, and 5 (26.3%) had progressive disease (5 of 24 patients [20.8%] were lost to follow-up). There was no association between a partial response and the presence of a BAP1 alteration, PD-L1 positivity, or nonepithelioid histology. With a median follow-up of 29.2 (95% CI, 19.3 to not available [NA]) months, the median PFS was 4.9 (95% CI, 2.8-13.3) months and the median OS was 20.9 (95% CI, 10.0 to NA) months from pembrolizumab initiation. Three patients (12.5%) experienced PFS of more than 2 years. Among patients with nonepithelioid vs epithelioid histology, there was a numeric advantage in median PFS (11.5 [95% CI, 2.8 to NA] vs 4.0 [95% CI, 2.8-8.8] months) and median OS (31.8 [95% CI, 8.3 to NA] vs 17.5 [95% CI, 10.0 to NA] months); however, this did not reach statistical significance.Conclusions and RelevanceThe results of this retrospective dual-center cohort study of patients with DMPM suggest that pembrolizumab had clinical activity regardless of PD-L1 status or histology, although patients with nonepithelioid histology may have experienced additional clinical benefit. The partial response rate of 21.0% and median OS of 20.9 months in this cohort with 75.0% epithelioid histology warrants further investigation to identify those most likely to respond to immunotherapy.

PURPOSE MET exon 14 skipping alterations ( METex14) comprise a diverse set of actionable oncogene drivers in non–small-cell lung cancer (NSCLC). Recent studies have established the efficacy of tyrosine kinase inhibitors for this patient population. The landscape of co-occurring genetic alterations in METex14 NSCLC and their potential impact to therapeutic sensitivities has not yet been fully described. MATERIALS AND METHODS METex14 NSCLC cases were collected from three cohorts: the VISION trial, and data sets from Guardant360 and GenePlus. Clinicopathologic characteristics and METex14 mutation sites were analyzed and compared across data sets. Co-occurring genetic alterations and the clonality relationships to METex14 were evaluated. RESULTS Of 40,824 NSCLCs, 692 METex14 cases (1.7%) were identified, including 332 in Guardant360, 188 in VISION, and 172 in GenePlus. The demographics and mutation type and/or sites were similar in the Asian versus Western cohorts. MET amplification, which were found to be associated with sensitivity to MET kinase inhibitors, co-occurs in 7.6%-13.8% of cases, whereas kinase domain secondary mutation of MET co-occurs in 5%-6%. When co-occurring with METex14, EGFR mutations were often identified as the dominant clone (78%, 7 of 9), whereas when co-occurring, METex14 (39%, 7 of 18) and KRAS (44%, 8 of 18) had similar rates of clonal dominance. PIK3CA and PTEN mutations were almost always subclones (89%, 16 of 18) to METex14. Moreover, RET-CCDC6 fusion and EGFR mutation were detected following crizotinib treatment in two patients, suggesting novel mechanisms of resistance. CONCLUSION METex14 mutations frequently co-occur with other potential driver oncogenes with differing patterns of clonal dominance observed among the drivers. This cellular context can provide insights into whether METex14 is acting as a primary oncogenic driver or resistance mechanism and help guide treatment choices.

8557 Background: Among patients with malignant mesothelioma, pembrolizumab has demonstrated activity in diffuse pleural mesothelioma (DPM), with limited data available for those with diffuse malignant peritoneal mesothelioma (DMPM). DMPM represents a clinically distinct entity from DPM and disease specific outcomes data is needed. We present real world data on the efficacy of pembrolizumab in DMPM. Methods: In this retrospective study, we identified patients with DMPM treated with pembrolizumab at two tertiary care cancer centers between 1/1/2009 and 1/1/2021. Clinicopathologic features were annotated. Median progression free survival (mPFS) and median overall survival (mOS) were calculated using Kaplan-Meier curves. Best overall response rate (BOR) was determined using RECIST 1.1 criteria. Association of partial response with disease characteristics was evaluated using Fisher’s exact test. Results: We identified 24 patients with DMPM who received pembrolizumab (median age 62 years, 63% never smokers, 58% female, 75% had epithelioid histology). All patients received systemic chemotherapy prior to pembrolizumab (median prior lines of therapy: 3). BOR was 17% (3 partial responses, 10 stable disease, 5 progressive disease, 6 lost to follow-up). With a median follow up time of 29.2 months, mPFS was 4.9 months and mOS 20.9 months from pembrolizumab initiation. Three patients experienced PFS of > 2 years. Among the 14 patients who underwent next generation sequencing of tumor tissue, there were 8 somatic BAP1 alterations. Among the 17 patients tested for PDL1, 6 had positive PDL1 expression (1-80%). There was no association between partial response and presence of a BAP1 somatic alteration (p = 0.453), PDL1 positivity (p = 0.7) or non-epithelioid histology (p = 0.55). Conclusions: Pembrolizumab is active in a PDL1 unselected cohort of patients with DMPM. The overall response rate of 17% and mPFS of 4.9 months in this 75% epithelioid histology cohort warrants further investigation to identify those most likely to respond to immunotherapy, especially among epithelioid histology.

BACKGROUND Little is known about recent trends in surveillance among the more than 1 million US colorectal cancer (CRC) survivors. Moreover, for stage I disease, which accounts for more than 30% of survivors, the guidelines are limited, and the use of surveillance has not been well studied. Guidelines were changed in 2005 to include recommendations for computed tomography (CT) surveillance in select patients, but the impact of these changes has not been explored. METHODS A retrospective analysis of patients who were identified in the Survival, Epidemiology, and End Results–Medicare database and underwent resection of stage I to III CRC between 2001 and 2009 was performed. The receipt of guideline-determined sufficient surveillance, including office visits, colonoscopy, carcinoembryonic antigen (CEA) testing, and CT imaging, in the 3 years after resection was evaluated. RESULTS The study included 23,990 colon cancer patients and 5665 rectal cancer patients. Rates of office visits and colonoscopy were high and stable over the study period. Rates of CEA surveillance increased over the study period but remained low, even for stage III disease. Rates of CT imaging increased gradually during the study period, but the 2005 guideline change had no effect. Stage II patients, including high-risk patients, received surveillance at significantly lower rates than stage III patients despite similar recommendations. Conversely, up to 30% of stage I patients received nonrecommended CEA testing and CT imaging. CONCLUSIONS There continues to be substantial underuse of surveillance for CRC survivors and particularly for stage II patients, who constitute almost 40% of survivors. The 2005 guideline change had a negligible impact on CT surveillance. Conversely, although guidelines are limited, many stage I patients are receiving intensive surveillance. Cancer 2015;121:3435–43. © 2015 American Cancer Society.