Nonendocrine Cancers Associated with Benign and Malignant Parathyroid Tumors.

Context: There are limited reliable epidemiological data concerning whether individuals with benign/malignant parathyroid tumor are at an elevated risk of developing nonendocrine malignancies or vice versa. Objective: The objective of the study was to quantify these risks, especially risk of parathyroid tumors after other cancers. Design: This was a population-based retrospective cohort study. Participants: Participants included the Swedish Family-Cancer Database (1958-2008; 11,697,301 individuals; 1,128,735 survivors of first primary cancers including 12,037 patients with parathyroid adenoma and 83 parathyroid adenocarcinoma). Main Outcome Measure: Standardized incidence ratios (SIR) were adjusted for age; sex; period; residential area; socioeconomic status; and history of hospitalization for obesity, alcoholism, or chronic obstructive pulmonary disease. Results: Nonendocrine cancer sites with significantly increased risk after parathyroid adenoma were small intestine (SIR 2.3), blood (polycythemia vera 2.0), kidney (1.8), nervous system (1.6), skin (melanoma 1.4), and breast (women 1.2). Risk of parathyroid adenoma significantly increased after polycythemia vera (3.9) and malignancy in small intestine (3.5), kidney (2.8), nervous system (2.0), prostate (1.5), skin (melanoma 1.5), bladder (1.4), and breast (women 1.2). Twelve cases of parathyroid adenocarcinoma showed significantly higher risk after other tumors (2.4), especially after thyroid cancer (46.6) and parathyroid adenoma (27.3) but not vice versa in 11 cancer survivors. Conclusions: Parathyroid adenoma can be a risk factor for parathyroid adenocarcinoma; polycythemia vera; melanoma; and small intestine, kidney, nervous system and breast cancers. Further studies are suggested to find underlying mechanisms for these elevated risks, especially for increased risk of parathyroid tumor in patients with melanoma polycythemia vera, or malignancy in small intestine, kidney, nervous system, bladder, prostate, or breast.