THE ROLE OF FDG-PET IN STAGING AND TREATMENT FOR STAGE III NSCLC IN ONTARIO BETWEEN 2009-2017

ABSTRACT

Purpose: Fluoro-2-deoxyglucose positron-emission tomography (PET) is now considered standard of care in the staging evaluation for new cases of Stage III NSCLC however, there is not level 3 evidence demonstrating efficacy of PET. Using retrospective population-based data, we sought to examine the role and timing that PET scans play in influencing treatment choice, as well as survival in patients treated with chemoradiation (CRT) for Stage III NSCLC. Materials and Methods: A retrospective cohort of patients diagnosed with Stage III NSCLC from 2009-2017 in Ontario were identified from the Institute of Clinical Evaluative Sciences (ICES). Overall survival (OS), using a landmark analysis of six months, was explored in the entire cohort (PET versus no PET) as well as in patients who received CRT for Stage III disease. Survival time was calculated using Kaplan Meier methods, logistic regression was used to evaluate type of treatment received, and Cox regression was used to evaluate factors prognostic of OS amongst patients who received CRT. Results: A total of 13 796 cases were included in our analysis: 6536 patients underwent PET scanning prior to treatment and 7260 did not. Over time, there was a significantly increased utilization of PET from 12.4% in 2009 to 74.1% in 2017 (p<0.001). In regard to treatment modality, significantly more patients received curative intent therapy in the PET group including CRT (1472 versus 939 patients;p<0.001), and surgery (1483 versus 734 patients;p<0.001). There was significantly improved OS in the whole cohort with upfront PET versus not with median OS of 17.1 (95% CI=16.3-17.8) versus 11.2 (10.6-11.9) months (p<0.001). In patients specifically receiving CRT, OS was similarly improved in the PET versus no PET subgroups with median OS of 21.7 (19.7-24.2) versus 18.5 (16.8-20.7) months (p=0.004). Examining the timing of PET scan and commencement of therapy, no significant difference was found among patients who had their scan <28 days prior to treatment (median OS =16 months), 2956 days prior to treatment (17.8 months), and >56 days prior to treatment (18.6 months), (p=0.38);these results were similar in the CRT only subgroup. On multivariate analysis, the only factors predicting survival in the CRT group were male gender (HR 1.20;1.08-1.33), increasing age (HR 1.07;1.04-1.10), surgery as part of trimodality therapy (HR 0.60;0.52-0.70), and receipt of PET prior to treatment (HR 0.83;0.72-0.95). Conclusions: Significant differences in treatment received and OS due to receipt of PET may be due to stage migration or unmeasured confounders. However, in a CRT subgroup, receipt of PET was associated with improved OS. Advocating for increased access to PET scans in this patient population is of utmost importance especially now with an additional survival benefit of adjuvant immunotherapy following CRT. The timing of the PET scan relative to initiating treatment did not have an obvious impact on survival, which may be reassuring for centres that may lack the capability to perform timely scans or are experiencing delays due to the COVID-19 pandemic.