Tumor subtypes associated with prostate cancer (PCa) both as first and second primary tumors: A registry-based analysis.

Abstract

e17528 Background: First primary tumors (FPT) generally are associated with decreased survival and, thus, reduced risk of second primary tumors (SPT). A greater than expected incidence of SPT may indicate causal factors shared in common with a particular FPT, especially if the converse also is observed, i.e. if incidence is also greater than expected when tumor sequence is reversed. We analyzed the Surveillance, Epidemiology, and End Results (SEER) cancer registry to identify tumors with higher than expected incidence in relation to PCa, both as FPT and SPT. Methods: We searched the SEER18 cancer database covering 18 geographical regions of the U.S. from 2000 to 2016. SEER*Stat software v.8.3.6 was used to calculate standardized incidence ratios (SIR) of various SPT after defined FPT. SIR compare the incidence of a particular cancer within subsets of the registry population as a ratio to the expected incidence from a comparable matched group derived from the general population. 813,712 men with prostatic FPT (1° PCa) were included in the analysis for SIR of any SPT, while 2,554,835 men with any FPT were included in the analysis for SIR of prostatic SPT (2° PCa). Results were stratified by race and latency. Reciprocal SIR (1° PCa; 2° PCa) for values with p < 0.05 are reported. Results: Aggregate analysis of all tumors demonstrated lower than expected SIR for SPT, both for any SPT after 1° PCa and for 2° PCa after any FPT (0.69; 0.53). By contrast, six tumor subtypes – small intestine (1.17; 1.19), melanoma (1.05; 1.23), bladder (1.14; 2.02), kidney (1.22; 1.36), thyroid (1.27; 1.36), and chronic myelogenous leukemia (1.10; 1.15) – had bidirectionally increased secondary SIR in relation to PCa. The reciprocal increases were detected across racial subgroups for bladder, kidney and thyroid cancers. SIR tended to be highest in the early post-FPT period (2-11 mo.) with significant increases for bladder (1.49; 6.75), kidney (2.66; 1.87), and thyroid (1.61; 1.65) cancers. These three tumor types retained bidirectional increases in relation to PCa over intermediate latencies (12-119 mo.), but not beyond 120 mo. Conclusions: Overall, FPT were associated with lower than expected incidence of SPT, most likely as a result of shortened life expectancy. However, several tumors were identified that 1). occurred with higher than expected incidence after 1° PCa and 2). were associated with higher than expected incidence of 2° PCa. Further examination of the relationship of these tumors with PCa may identify mutual intrinsic or extrinsic factors that contribute to tumor development.