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S. Mahale

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    MO10 - Molecular Pathology II (ID 127)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Pathology
    • Presentations: 1
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      MO10.10 - Detection of RET fusions by FISH in unselected NSCLC (ID 2434)

      16:15 - 17:45  |  Author(s): S. Mahale

      • Abstract
      • Presentation
      • Slides

      Activation of the RET gene by fusion has been described in 1-2% of unselected population of non-small-cell lung cancer (NSCLC) and there is early evidence suggesting that patients with RET activated tumors obtain clinical benefit from RET inhibitors. The major fusion partner is KIF5B, but CCDC6, NCOA4 and TRIM33 have also been reported. The prevalence of RET fusions in different lung cancer subtypes and clinicopathologic characteristics of remain unclear. In this study, we sought to identify RET rearrangements in NSCLC using FISH and to investigate the association with histology and clinical features.

      A 3-target, 3-color FISH probe set [3’RET in red, 5’RET in green, 5’KIF5B in yellow] was developed to simultaneously detect (a) disruption between 3’ and 5’ RET and (b) specific fusion between 5’KIF5B-3’RET. This probe set was used to interrogate a cohort of Caucasian NSCLC patients using tumor microarray. Inclusion of specimens on the tissue microarray was independent of gender, age, smoking history, histology and any known molecular profile and was only based on patient informed consent and tissue availability.

      Among 348 evaluable NSCLC patients, 6 (1.7%) were found to be positive for RET rearrangement (RET+): 2 showed typical KIF5B:RET pattern, 2 showed patterns consistent with CCDC6: RET fusion; and 2 had split 3’-5’ without suggestion of the fusion partner identity. The histology was adenocarcinoma in 4, large cell carcinoma in 1 and squamous cell carcinoma in 1. All RET+ tumors were wild type for EGFR and negative for ALK and ROS1 rearrangements. The mean age of RET+ patients at the time of diagnosis was 62 years (49-74) and they were predominantly male (5) and former (4) or current smokers (1). The 10p11-q11 region displayed high level of genomic instability, with RET doublets, KIF5B and RET doublets, unbalanced KIF5B copy number gain, fusion KIF5B with 5’ and 3’RET, and abnormal separation between KIF5B and RET in 8.5%, 5.1%, 9.6%, 2.3%, and 2% of specimens, respectively. These atypical patterns will be further investigated by RT-PCR.

      The customized 3-target, 3-color probe set successfully detected KIF5B:RET rearrangements and identified patterns suggestive of RET rearrangements with non-KIF5B partners in small subset of unselected NSCLC. Interestingly, only a minority of RET + patients were never smokers and 1/3 of them had non-adenocarcinoma histology. Despite the benefits of using enrichment strategies based on clinicopathologic variables for molecular testing of NSCLC in search for personalized therapy, these findings argue against using variables such as smoking status and histology for screening selection when the aim is to detect all potential RET+ patients.

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