The exact risk of multiple primary neoplasms in patients with salivary gland or thyroid gland malignancies is difficult to ascertain from the data available in the literature. This study examines, retrospectively, 198 patients with a first malignancy of the salivary gland and 186 patients with a first malignancy of the thyroid gland, treated over a 10-year period. Fourteen cases of second tumors were found in the first group and 29 cases in the latter. Patients whose second neoplasm was a skin cancer or who had a previous neoplasm at a site other than those selected for study were excluded. The risk of a second tumor was compared to the expected number of second cancers from the Combined National Cancer Institute Registry Data, and the results indicated an increased risk in males with a first malignancy of the salivary gland and in both men and women with a first thyroid malignancy. The salivary glands, larynx, and colon were the most common sites of second tumors after a first salivary cancer. The adrenals, brain, lymphatic system, and breast were the most common site after a first thyroid cancer. The previously reported association of cancers of the thyroid and the breast in females is confirmed here in men and women. The excess of brain tumors and lymphomas has not been reported previously.
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