Increased risk of malignant diseases after surgery for primary hyperparathyroidism. A nationwide cohort study.

A cohort of 4,163 persons reported to the nationwide Swedish Cancer Registry by reason of hyperparathyroidism was followed for up to 22 completed years (24,593 person-years of observation). The occurrence of malignant disease manifested after parathyroid surgery was investigated through computerized linkage to the entire Cancer Registry. During the entire period, the hyperparathyroidism patients suffered malignant diseases significantly more often than the background population (relative risk (RR) = 1.6, 95% confidence interval (CI) 1.5-1.8). Even if all cases with malignant diseases detected at the same time as hyperparathyroidism or during the first year after parathyroid surgery were eliminated, a significantly increased risk remained for the following years (RR = 1.4, 95% CI 1.2-1.6). A significantly increased relative risk of developing gastrointestinal cancers, endocrine tumors, kidney carcinomas, and mammary carcinomas was found. During the first postoperative year, an increased surveillance of the cohort is likely to have contributed to the increased risk, but detection bias is considered unlikely to be the only explanation for the higher risk during all subsequent years. The findings indicate that hyperparathyroidism either promotes later development of malignant tumors or that this condition and certain malignant diseases have etiologic factors in common.