We revealed a negative and significant association between the pre-IMRT IgA concentration and OM maximum severity during cancer treatment, indicating that patients with lower pre-IMRT IgA saliva concentrations could be more prone to develop grade 2 and 3 OM (grade 2 and 3 mean IgA concentration: 10.4; grade 1 mean IgA concentration: 17.7). The gene discussed is CD79A; the disease is cancer.