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A. Dowlati



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    OA 18 - Lung Cancer Pathology and Genetics (ID 687)

    • Event: WCLC 2017
    • Type: Oral
    • Track: Biology/Pathology
    • Presentations: 1
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      OA 18.03 - Genomic Profiling Reveals Hedgehog Pathway Alterations in Vismodegib Sensitive Lung Squamous Cell Carcinoma (ID 10599)

      14:50 - 15:00  |  Author(s): A. Dowlati

      • Abstract
      • Presentation
      • Slides

      Background:
      The objective response rate of squamous cell carcinoma of the lung (SCCL) to checkpoint inhibitors, as well as the frequency of known NSCLC oncogenic drivers, is low. We performed comprehensive genomic profiling (CGP) on a large set of SCCL cases to identify new opportunities for potential benefit from targeted or immunotherapies.

      Method:
      Hybrid-capture based CGP of up to 315 genes was performed prospectively on DNA isolated from tissue-based FFPE samples of SCCL, and tumor mutational burden (TMB) was assessed as described previously (PMID: 28420421).

      Result:
      From a dataset of 958 unique SCCL cases, we identify 2.6% of cases harboring alterations in PTCH1, 0.3% in SMO1, and 01.2% in SUFU, which were primarily mutually exclusive Genes known to be oncogenic drivers in NSCLC were altered at the following frequencies in SCCL 8.0% KRAS, 6.8% EGFR, 3.4% MET, 1.9% BRAF, and less than 1% each for ALK, ROS, and RET. In PTCH1-mutated cases 96% did not harbor alterations in these driver genes (1/23 positive for co-occurrence).. The overall SCCL population has a median TMB of 9.0, with 11.3%) cases higher than 20 mutations/Mb (m/Mb). Two index cases with PTCH1 mutations and no alterations in established NSCLC driver genes were identified. A year 77-year-old male with a 40 pack-year smoking history was diagnosed with metastatic SCCL, basaloid variant, harboring PTCH1 s799fs*29 with TMB of 3.7 m/Mb, and he had a year-long complete response to vismodegib. A 69-year-old male with poorly differentiated SCCL harboring PTCH1 W197* and W460* had a 7 month response to vismodegib. On progression, biopsy of recurrent disease after vismodegib failure demonstrated the same PTCH1 alterations as well as acquisition of the 11q13 (CCND1/FGF3/FGF4/FGF19) amplicon. Both biopsies had TMB > 45 m/mb. Nine additional cases not in this series identified as the basaloid variant of SCCL by expert thoracic pathology review were assayed by CGP and 11% (1/9) harbored PTCH1 mutation, but no other alterations of the hedgehog pathway were identified.

      Conclusion:
      The index cases presented here suggest a subset of PTCH1-mutated SCCL may see clinical benefit from hedgehog inhibitors, regardless of TMB. In a small series of expert diagnosed basaloid histology in SCCL cases, this histology may enrich for hedgehog pathway alterations. Further investigation of underlying PTCH1 LOH and TMB will be undertaken to assess which SCCL cases can respond to respond to hedgehog pathway inhibitors.

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