2ND PRIMARY NEOPLASMS IN THYROID-CANCER PATIENTS

To determine risk patterns for second primary neoplasms after the occu rrence of thyroid cancer, we conducted a retrospective cohort study of 3321 thyroid cancer patients who were operated and histologically con firmed at the Noguchi Thyroid Clinic and Hospital Foundation between 1 946 and 1985. They were followed from the date of operation through th e end of 1990 with an observation period from 45 to 5 years. The avera ge observation period of the patients was 13.4 years and the follow-up rate reached 98%. The standardized mortality ratio (SMR) was computed to assess possible risk increase by cancer site. In this computation, the time period less than 5 years after operation was omitted to redu ce the influence of deaths related to the original thyroid cancer. A t otal of 103 deaths from malignant neoplasms other than thyroid cancer were observed during this time period (SMR = 1.6, 95% confidence inter val [CI] = 1.3-2.0). Analyses of site-specific cancer mortality reveal ed significantly elevated risks for the central nervous system (SMR = 16.1, CI = 5.2-37.6) and respiratory organs (SMR = 2.6, CI = 1.5-4.1). Based on a review of available medical records with histological find ings, we concluded that the risk increases for these sites were most l ikely to be attributable to second primary neoplasms. Whether or not t he patients had received radiotherapy was not significantly associated with elevated risk. Further investigations are needed to clarify the risk factors responsible for the above findings.