Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized disease, characterized by high serum
IgG4 concentrations and IgG4-producing plasma cell expansion with fibrotic or sclerotic changes in affected organs. Recent work has focused on the relationship between
IgG4-RD and
malignancies, but there is no report of
malignancies associated with
IgG4-RD in head and neck regions. The aim of this study was to analyze the clinicopathological characteristics of
malignancies in patients with
IgG4-RD in head and neck regions. We retrospectively analyzed 26 patients with
IgG4-RD (12 men and 14 women aged 60.6 ± 11.6 years). The mean follow-up period was 26.6 months (from 12 to 96 months). These patients were divided into single-lesion group (n = 12) with
IgG4-RD only in head and neck regions and multiple-lesion group (n = 14) with
IgG4-RD in other regions. There was no significant difference in serum
IgG4 concentrations between the single-lesion group (459.4 ± 336.4 mg/dL) and the multiple-lesion group (908.0 ± 739.2 mg/dL) (P = 0.07), whereas the
IgG4/
IgG ratio was significantly lower in the single-lesion group (22.8 ± 11.0%; n = 11) compared with the multiple-lesion group (31.7 ± 15.0%; n = 11, P = 0.02). Among the 26 patients, two patients (7.7%), both in the multiple-lesion group, developed life-threatening
malignancies (salivary duct
carcinoma in the submandibular gland and
lymphoma in the orbital tissue). All physicians need to keep in mind the possible coexistence of
malignancies in patients with
IgG4-RD with high
IgG4/
IgG ratio and multiple lesions at the time of diagnosis.