Second primary lung cancer (SPLC) occurs at a rate of 1-2% per year in nonsmall cell lung cancer (NSCLC) patients following surgical resection. Wang and colleagues examined patterns of second primary lung cancer in patients undergoing CT scans at fixed 6-month intervals during the first 2 years. All patients in their study but one had the second primary lung cancer identified at the asymptomatic stage (Y. Wang et. al). It is critical to detect SPLC when asymptomatic as presence of symptoms at diagnosis is associated with detection at later stage and worse overall survival (L. Calman et. al)( F. Lou et. al). With increasing implementation of stereotactic ablative radiotherapy (SABR) for medically inoperable, early stage NSCLC, improved understanding of SPLC in this population is important.

Introduction/background

Second primary lung cancers (SPLC) are common following non-small cell lung cancer (NSCLC) treatment. Development of SPLC following stereotactic ablative radiation therapy (SABR) may differ as compared to surgical cohorts. We report incidence of and outcomes for SPLC detected by surveillance imaging in a cohort of patients treated with SABR.

Materials/methods

Patients treated with SABR for node-negative NSCLC between February, 2007 to May, 2019 were retrospectively identified. Patient characteristics, frequency of surveillance imaging, development of SPLC, recurrence patterns, and survival were reviewed. Surveillance CT was performed Q3-4 month year 1, Q3-6 month year 2, Q6-12 month year 3-5, and Q12 month thereafter. Actuarial estimates of development of SPLC and overall survival (OS) were generated with competing risk analysis.

Results

We identified 134 patients treated with SABR with ≥6 months follow up. Eighteen (13.4%) developed a total of 21 SPLC at a median of 28.5 months (range 3.0-84.7 months) following SABR, 19 (90.5%) biopsy-proven. Twenty (95.2%) SPLC were detected by surveillance imaging. Three patients developed 2 metachronous SPLC. Three and 5 year SPLC estimates were 11.7% and 13.1%. Eighteen (85.7%) SPLC were treated with curative intent. Two and 3 year estimate of OS following detection of SPLC was 79.8% and 54.7%.

Conclusion

SPLC were more common in our cohort than other published studies. Outcomes following surveillance detected SPLC are similar to those of de novo early stage lung cancers. The high frequency of SPLC in our cohort suggests further studies to refine overall surveillance in very high-risk populations are needed.