Primary cancers before and after prostate cancer diagnosis.

BACKGROUND: The occurrence of multiple cancers may indicate common etiology; and, although some studies have investigated the risk of second primary cancers after prostate cancer (PCa), there are no studies on cancers before PCa.
METHODS: The PCBaSe Sweden database is based on the National Prostate Cancer Register (NPCR), which covers >96% of PCa cases. The authors estimated the prevalence and cumulative incidence of different cancers before and after PCa diagnosis in 72,613 men according to PCa treatment and disease stage in PCBaSe and their matched comparison cohort of men who were free of PCa.
RESULTS: In total, 6829 men were diagnosed with another primary cancer before their PCa diagnosis, including 138 men at the time of PCa diagnosis and 5230 men were diagnosed after PCa diagnosis. Cancer of the bladder or colon and nonmelanoma of the skin were the 3 most frequently observed cancers before and after PCa diagnosis. At the time of PCa diagnosis, the prevalence of these 3 cancers was 1.94% for bladder cancer, 1.08% for colon cancer, and 1.08% for nonmelanoma skin cancer, compared with 1.30%, 0.96%, and 1.03%, respectively, for the matched comparison cohort. Five years after PCa diagnosis, the difference in incidence proportion between PCa men and their comparison cohort was 7 ‰ (95% CI, 5.6 ‰-8.5 ‰), 1.3 ‰ (0 ‰-2.6 ‰), and 1.6 ‰ (0.6 ‰-2.6 ‰) for these 3 cancers, respectively. From a uro-oncologic point of view, it is interesting to note that the prevalence of kidney cancer at the time of PCa diagnosis was 0.42% compared with 0.28% for the matched comparison cohort.
CONCLUSIONS: Approximately 17% of all PCa occurred in combination with another primary cancer (before or after PCa diagnosis). Detection bias probably explains part of this observation, but further investigations are required to assess possible underlying mechanisms.