Author of

• 12648

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  P3.11 - Poster Session 3 - NSCLC Novel Therapies (ID 211)

  • Event: WCLC 2013
  • Type: Poster Session
  • Track: Medical Oncology
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/30/2013, 09:30 - 16:30, Exhibit Hall, Ground Level

  • 12692

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    P3.11-044 - Clinical impact of EGFR mutation fraction and tumour cellularity in EGFR mutation positive NSCLC (ID 2982)

    09:30 - 09:30  |  Author(s): S. Cheng
    • Abstract

    Background
    We investigated the impact of mutation fraction, tumour sample cellularity, and diagnostic specimen type on EGFR TKI response, time to treatment failure (TTF) and overall survival (OS), as well as patterns of treatment in a population-based cohort of advanced EGFR mutation positive NSCLC patients.

    Methods
    From March 2010 to May 2012, EGFR testing in the province of Ontario (Canada) was conducted at a single centre, using fragment analysis for exon 19 deletion and Sau961 restriction enzyme digest for exon 21 mutations. Patients with EGFR mutation positive samples were identified and tumour sample cellularity, mutation fraction (percent of tumour cells mutated), demographic, treatment and outcome data were collected. Regression analysis was undertaken to assess the association between demographic variables, mutation fraction, tumour sample cellularity and sample type on clinical outcomes.

    Results
    Among 293 patients identified with EGFR mutation positive NSCLC, 253 received EGFR TKIs and are included in this analysis. Most are female (72%), never smokers (59%), have exon 19 deletions (53%; 47% exon21 L858R), and median age 65 years (range 26 to 96). Tumour specimens tested include resection (32%), cytology (30%), and core biopsies (38%). Median EGFR mutation fraction is 30% (range 0.4% to 96%); 24% had a low (≤10%) mutation fraction, and 13% had a mutation fraction ≤5%. Responses (any tumour reduction) were seen in 62%, mixed response or stable disease in 25%, and progression as the best response in 13%. Median TTF from the start of EGFR TKI therapy is 13.2 months (range 0-43.7 months). Median OS from TKI start is 22.3 months (95% CI: 19.5-28.2 months), with 1-, 2- and 3-year survival rates of 72%, 49% and 37%. In multivariable analysis, factors associated with TTF included female sex (HR 0.69, p=0.03) and sample type (resection HR 0.56, cytology HR 0.82, core biopsy as reference, p=0.01). Age at metastatic diagnosis (p=0.01), sample cellularity (p=0.01) and sample type were significantly associated with OS, (resection HR 0.51, cytology HR 0.70, core biopsy as reference, p=0.04). Proportional odds logistic regression identified that mutation frequency and age at metastatic diagnosis were significantly associated with the odds of response, (p=0.047, p=0.04 respectively). Responses were seen even in those with lower EGFR mutation fraction, 48% (24/50) at a mutation frequency of ≤10% and 33% (9/27) at a mutation frequency of ≤5%. The average cellularity in the high (>10%) mutation fraction group was 53% (95%CI 50– 56%), and 36% (95%CI 29 – 43%) in those with a low mutation fraction (p<.0001).

    Conclusion
    Pathologic features may be relevant to clinical outcomes in EGFR mutation positive NSCLC, including mutation fraction, sample cellularity, and specimen tested. The clinical relevance of sample tumour cellularity and sample type tested remains unclear. In particular, initial stage and prognosis may be confounders in the association between resected specimens and favourable outcomes. Given that those with mutation fractions ≤5% may have significant response from EGFR TKI therapy, treatment should not be withheld on the basis of mutation frequency alone.