Schizophrenia cancer risk varies with disease duration, age at onset
medwireNews: The risk for cancer among patients with schizophrenia correlates inversely with the age of diagnosis and disease duration, say researchers, such that patients who develop late-onset schizophrenia have a lower cancer risk than the general population.
"The cancer risk peaked in the early deteriorating phase and gradually decreased as schizophrenia evolved into the later phases," report Yi-Hwei Li (Tzu-Chi University, Hualian City, Taiwan) and colleagues in Schizophrenia Bulletin.
The researchers analyzed 71,317 patients diagnosed with schizophrenia and 20,567 patients diagnosed with bipolar disorder between 1997 and 2009 using data from the Taiwan National Health Insurance database. The mean follow-up time was 6.7 years in the schizophrenia cohort and 5.6 years in the bipolar disorder cohort.
Overall, patients had an increased risk for cancer compared with the general population with a standardized incidence ratio (SIR) for all cancers of 1.17 in schizophrenia patients and 1.29 in bipolar disorder patients.
Among patients with schizophrenia, however, the overall risk for cancer reduced gradually as the age disease onset increased, such that patients aged 20-29 years old had a 1.85-fold increased risk compared with the general population while those aged 60 years and over had a 23% reduced risk.
For patients who had a schizophrenia diagnosis before the age of 50 years, the risk for colorectal, breast, cervical, and uterine cancers was significantly increased. However, when diagnosed after this age, only the risk for breast cancer remained significantly elevated.
Time since diagnosis was associated with decreasing cancer risk, falling from an SIR of 22.9 within the first year to 0.30 after more than 10 years.
"Generally speaking, after 5 years of schizophrenia diagnosis, the cancer risk appeared significantly lower than that of the same-sex and similar age general population," the authors note.
The authors also noted gender differences in cancer risk. They found that women with schizophrenia had an increased risk for cancer compared with the general population (SIR=1.31) whereas men did not. In contrast, in those with bipolar disorder, men had an increased risk for cancer (n=1.42), but women did not.
There has been continued debate over the relationship between cancer risk and schizophrenia, the authors explain. They suggest that middle- and late-diagnosed patients may be protected from cancer by biologic characteristics such as Wnt pathway inactivation, dopamine effects, and enhance natural killer cell activity. Meanwhile, the anticarcinogenic effects of antipsychotics could be responsible for the lowered cancer risk among long-term schizophrenia patients.
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