Overestimated risk of second primary malignancies in ovarian cancer patients

Registry-based cohort studies have established an increased risk of developing second primary malignancies (SPM) in patients with a primary ovarian cancer. In order to examine the accuracy of cancer registration with emphasis on registration of SPM, 344 women with ovarian cancer and 379 subsequent SPM, registered between 1958 and 1992 in the Stockholm-Gotland Cancer Registry (SGCR), a division of the Swedish Cancer Registry (SCR), were investigated. Complete records including pathology reports were examined and an additional histopathological evaluation was conducted for a sample of the group. The results revealed that 28 diagnoses of SPM were incorrectly registered (14 cases were misdiagnosed SPM of the gastrointestinal tract, mainly colon and rectum) and 34 women (with 38 SPM) were incorrectly registered with ovarian cancer. Recalculations of the risk of a subsequent cancer were performed on the basis of these findings and the results suggest an overestimation of the risk of developing SPM. Inferences of these findings to other primary sites of multiple malignancies should be made with caution and further studies are needed.