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Inverse association between cancer risks and age in schizophrenic patients: A 12‐year nationwide cohort study

The association between schizophrenia and cancer risk is contentious in the clinical and epidemiological literature. Studies from different populations, tumor sites, or health care systems have provided inconsistent findings. In the present study, we examined a less well‐investigated hypothesis that age plays a crucial role in cancer risk in schizophrenia. We conducted a nationwide cohort study using Taiwan's National Health Insurance Research Database (NHIRD) between 1995 and 2007. Overall, gender‐, and age‐stratified standardized incidence ratios (SIR) were used to investigate the pattern of cancer risk by age. Of the 102 202 schizophrenic patients, 1738 developed cancer after a diagnosis of schizophrenia (SIR = 0.92; 95% confidence interval [CI] 0.90–0.96). However, the age‐stratified SIR declined with age (e.g. SIR [95% CI] = 1.97 [1.85–2.33], 0.68 [0.65–0.78], and 0.36 [0.34–0.45] for those aged 20–29, 60–69, and ≥70 years, respectively) in both genders and for major cancers. Cancer risks in schizophrenic patients were lower for cancers that are more likely to develop at an older age in the general population (e.g. stomach cancer [SIR = 0.62; 95% CI 0.57–0.80], pancreatic cancer [SIR = 0.49; 95% CI 0.39–0.84], and prostate cancer [SIR = 0.35; 95% CI 0.29–0.58]). In contrast, cancer risks were higher for cancers that have a younger age of onset, such as cancers of the nasopharynx (SIR = 1.18; 95% CI 1.08–1.49), breast (SIR = 1.50; 95% CI 1.44–1.66) and uterine corpus (SIR = 2.15; 95% CI 1.98–2.74). The unique age structures and early aging potential of schizophrenia populations may contribute to the observed inverse relationship between age and cancer risk. Higher cancer comorbidity in young schizophrenic patients deserves more attention.