Development of multiple primary cancers in lung cancer patients: Appalachian versus non-appalachian populations of Kentucky

Objectives The aim of this study was to investigate whether patients with lung cancer in Appalachian Kentucky are more likely to develop multiple primary cancers than patients in non-Appalachian Kentucky. Additional analyses were conducted to identify other factors that may be associated with an increased hazard of developing multiple primary cancers in patients with lung cancer. Methods The data for this retrospective, population-based cohort study of 26,456 primary lung cancer patients were drawn from the Kentucky Cancer Registry. For inclusion in the study, patients must have been diagnosed between January 1, 2000 and December 31, 2013 and they must either have continually resided in Appalachian Kentucky or continually resided in non-Appalachian Kentucky. Cases were excluded if the patient was diagnosed as having additional primary cancers within 3 months of the initial diagnosis of primary lung cancer. The medical records for each case were examined to determine whether the patient was subsequently diagnosed as having additional primary cancers. The Cox proportional hazards model was then used to assess whether there was an association between the region in which the patients live and the likelihood of developing multiple primary cancers. Time to event was considered as the time from diagnosis to either death or development of a second primary cancer. Results The results presented here indicate that the risk of developing multiple primary cancers is the same for patients with lung cancer throughout Kentucky (hazard ratio [HR] 1.002, P = 0.9713). We found no evidence for a greater hazard in patients from Appalachia; however, additional analyses revealed several high-risk groups. Male patients and older patients had a significantly greater hazard of developing multiple primary cancers (HR 1.169, P = 0.012 and 1.015, P = 0.0001, respectively). In addition, patients who underwent surgery and those who were diagnosed initially as having an earlier stage of cancer also were more likely to develop multiple primary cancers (HR 1.446, P = 0.0003 and 0.684, P = 0.0015, respectively). Conclusions This is a negative study. Patients with primary lung cancer living in Appalachian Kentucky are not at a greater risk of developing multiple primary cancers than those residing in non-Appalachian Kentucky. High-risk groups identified in this study are male patients and older patients. The increased hazard seen in patients who underwent surgery or those who were diagnosed as having earlier stages of lung cancer are likely an artifact of these patients living longer and, therefore, having more time to develop additional primary cancers.