A practical molecular assay to predict survival in resected non-squamous, non-small-cell lung cancer: development and international validation studies

Abstract

Background: The frequent recurrence of early-stage non-small-cell lung cancer (NSCLC) is generally attributable to metastatic disease undetected at complete resection. Management of such patients depends on prognostic staging to identify the individuals most likely to have occult disease. We aimed to develop and validate a practical, reliable assay that improves risk stratification compared with conventional staging.

Methods: A 14-gene expression assay that uses quantitative PCR, runs on formalin-fixed paraffin-embedded tissue samples, and differentiates patients with heterogeneous statistical prognoses was developed in a cohort of 361 patients with non-squamous NSCLC resected at the University of California, San Francisco. The assay was then independently validated by the Kaiser Permanente Division of Research in a masked cohort of 433 patients with stage I non-squamous NSCLC resected at Kaiser Permanente Northern California hospitals, and on a cohort of 1006 patients with stage I-III non-squamous NSCLC resected in several leading Chinese cancer centres that are part of the China Clinical Trials Consortium (CCTC).

Findings: Kaplan-Meier analysis of the Kaiser validation cohort showed 5 year overall survival of 71·4% (95% CI 60·5-80·0) in low-risk, 58·3% (48·9-66·6) in intermediate-risk, and 49·2% (42·2-55·8) in high-risk patients (p(trend)=0·0003). Similar analysis of the CCTC cohort indicated 5 year overall survivals of 74·1% (66·0-80·6) in low-risk, 57·4% (48·3-65·5) in intermediate-risk, and 44·6% (40·2-48·9) in high-risk patients (p(trend)<0·0001). Multivariate analysis in both cohorts indicated that no standard clinical risk factors could account for, or provide, the prognostic information derived from tumour gene expression. The assay improved prognostic accuracy beyond National Comprehensive Cancer Network criteria for stage I high-risk tumours (p<0·0001), and differentiated low-risk, intermediate-risk, and high-risk patients within all disease stages.

Interpretation: Our practical, quantitative-PCR-based assay reliably identified patients with early-stage non-squamous NSCLC at high risk for mortality after surgical resection.

Funding: UCSF Thoracic Oncology Laboratory and Pinpoint Genomics.

Figure 1. Probability of mortality and mortality hazard ratio by subgroup in the training cohort

Probability of mortality at 5 years by risk score; dashed lines are 95% CIs, hash marks above the x axis are individual risk scores for every patient. (B) Increase in 5 year overall mortality hazard ratio (HR) by subgroup for each stepwise increase in risk category (eg, low to intermediate, and intermediate to high); box sizes are proportional to group size. A hazard ratio greater than 1 implies that more patients in the high-risk group are dying at any time compared with the low-risk group; a hazard ratio of less than 1 means that fewer patients in the high-risk group are dying at any time compared with the low-risk group. AJCC=American Joint Committee on Cancer.

Figure 2. Survival analysis by risk category in the Kaiser Permanente validation cohort

(A) Overall survival for the entire cohort; median survival was 113 months in the low-risk group, 91 months in the intermediate-risk group, and 59 months in the high-risk group. (B) Lung-cancer-specific survival for the entire cohort (non-lung cancer deaths were censored); median lung cancer-specific survival was not reached in any risk group; the mortality incidence rate was 2·7 per 100 person-years in the low-risk group, 5·0 per 100 person-years in the intermediate-risk group, and 6·6 per 100 person-years in the high-risk group. (C) Overall survival for 330 patients with American Joint Commission on Cancer stage IA and IB disease considered to be low risk as per conventional pathological criteria (National Comprehensive Cancer Network); median survival was 113 months in the low-risk group, 88 months in the intermediate-risk group, and 70 months in the high-risk group.

Figure 3. Survival analysis by risk category in the China Clinical Trials Consortium validation cohort

(A) Overall survival for the entire cohort. Survival in patients with stage I (B) stage II (C) and stage III (D) disease.