Salivary gland tumors among atomic bomb survivors, 1950-1987

Malignant and benign tumors of the salivary glands have been associated with exposure to ionizing radiation from various sources, including the atomic bombings in Hiroshima and Nagasaki. However, questions remain unanswered regarding the nature and size of the risk and specific types of tumors involved.

The incidence and pathology of malignant and benign tumors of the salivary glands was studied in the Life Span Study cohort of atomic bomb survivors followed by the Radiation Effects Research Foundation (RERF) in Hiroshima and Nagasaki, Japan. Incident cases diagnosed during the period 1950-1987 were ascertained from the tumor and tissue registries of Hiroshima and Nagasaki and supplemented by additional case findings from autopsy, biopsy, and surgical specimens maintained at RERF and other institutions. Pathology slides and medical documents were reviewed by a panel of four pathologists who classified tumors using the World Health Organization classification scheme. Analyses were performed of histologic features associated with radiation exposure.

Of 145 tumors of the salivary glands identified (119 of the major and 26 of the minor salivary glands), 120 (83%) were histologically confirmed by the current investigators. Among 41 malignant tumors, the frequency of mucoepidermoid tumor was disproportionately high at high radiation doses (P = 0.04); among 94 benign tumors, the frequency of Warthin's tumor increased with increasing radiation dose (P = 0.06). The nature of the tumor was undetermined for the remaining ten cases. Mortality from malignant tumors of the salivary gland was inversely related to radiation dose, reflecting the predominance of mucoepidermoid carcinoma at high dose levels in this series. In one case with high radiation exposure, mucoepidermoid carcinoma of the parotid gland was accompanied by a preexisting or coexisting Warthin's tumor.

These findings, supported by population-based analyses in a companion study reported elsewhere, suggest a causal role for ionizing radiation in salivary gland tumorigenesis, particularly for mucoepidermoid carcinoma, and in the induction of one type of benign tumor (Warthin's tumor).