Objective: This study attempted to determine whether a genetic protection against cancer might be manifest in parents of offspring with schizophrenia.
Method: Using data from the Danish Central Population Registry, the authors identified 1,999,072 parents of offspring born after 1935. By linking this nationwide population-based parent cohort to the Danish Psychiatric Central Register, they identified 19,856 parents of offspring with schizophrenia. Follow-up for cancer in the Danish Cancer Registry began on the date of birth of the oldest child or April 1, 1969, and ended on the date of cancer diagnosis, death, or Dec. 31, 1997, yielding a total of 48,343,430 person-years at risk and 211,681 cases of cancer. The relative risk for cancer among parents with schizophrenic offspring compared to parents with no schizophrenic offspring was estimated by Poisson regression analysis and adjusted for age, period, and number of children.
Results: The risk for all cancer was 1.01 for fathers and 1.00 for mothers of schizophrenics. Mothers of schizophrenic patients had an increased risk of 1.20 for lung cancer and a nonsignificant risk of 1.14 for tobacco-related cancers combined. Apart from a reduced risk for leukemia in both mothers and fathers of schizophrenics, there was no difference in risk for any other cancer.
Discussion: This study does not confirm a previously reported reduced risk for cancer in parents of schizophrenic patients and provides no support for genetic protection against cancer in families with schizophrenia.