Gamma Radiation Sensitivity and Risk of Malignant and Benign Salivary Gland Tumors: A Pilot Case-Control Analysis

BACKGROUND. The salivary gland is a highly radiosensitive organ. Exposure to gamma radiation is a risk factor for both malignant (MSTs) and benign salivary gland tumors (BSTs), but the exact mechanisms remain unknown. The objectives of the current study were to determine whether gamma radiation-induced chromatid breaks increase the risk of MSTs and BSTs and whether there is any difference in risk between these two diseases. METHODS. The authors performed a pilot case-control study of 57 patients with salivary gland diseases (45 patients with MSTs and 12 patients with BSTs) and 105 cancer-free controls. Peripheral blood lymphocytes from these participants were cultured and exposed to gamma radiation (1.5 grays). Five hours later, metaphase spread slides were evaluated. The chromatid breaks in 50 well-spread metaphase slides were counted to determine the average number of chromatid breaks per cell (b/c). RESULTS. Multivariate logistic regression analyses revealed that gamma radiation-induced b/c values greater than the median of the controls were a significant risk factor for salivary gland tumors (adjusted odds ratio [OR], 17.25; 95% confidence interval [CI], 4.92-60.49). The risk remained significant for MSTs (adjusted OR, 40.45; 95% CI, 5.27-310.17) but was of borderline significance for BSTs (adjusted OR, 4.73; 95% CI, 0.94-23.87) when these tumors were analyzed separately. CONCLUSIONS. In the current study, high levels of chromatid breaks in lymphocytes induced by gamma irradiation were associated with an independent risk for MSTs and were likely to increase the risk of BSTs. However, larger studies are needed to verify these findings.