Hyperparathyroidism and subsequent cancer risk in Denmark

BACKGROUND. There is increasing evidence that hyperparathyroidism (HPT), a condition that leads to elevated serum calcium levels, is associated with endocrine and other malignancies, suggesting a possible causal link between HPT and carcinoma. METHODS. To investigate the relation of HPT to subsequent cancer risk, the authors conducted a record-linkage study among 2425 patients who were diagnosed with HPT in Danish hospitals. Patients were identified in hospital discharge records, and records were then linked with the Danish National Cancer Registry for the years 1977-1993 to identify cancer incidence. To estimate cancer risk, standardized incidence ratios (SIRs) were computed. RESULTS. After excluding patients who were diagnosed in the first year of follow-up, a total of 219 malignancies were observed, resulting in an SIR of 1.25 (95% confidence interval [95%CI], 1.1-1.4). Cancer risk among women was higher than among men. Among those with primary (idiopathic) HPT, hematopoetic malignancies were elevated significantly (SIR, 1.88; 95%CI, 1.0-3.2; based on 13 patients), with the excess derived primarily from 4 observed patients with multiple myeloma. Patients with secondary HPT had an insignificantly increased risk of overall cancers. Patients who were diagnosed with other or unspecified types of HPT had significant increases in carcinoma of the urinary tract (SIR, 2.71; 95%Cl, 1.2-5.3; based on 8 patients) and carcinoma of the thyroid gland (SIR, 21.19; 95%Cl, 4.3-61.9; based on 3 patients). CONCLUSIONS. Future studies should monitor whether specific endocrine alterations associated with HPT may affect the long-term risk of hematopoetic, thyroid, and urinary tract carcinomas.