Risks for malignancies in patients with chronic thyroiditis: a long-term follow-up study

As a typical autoimmune disease, chronic thyroiditis may impose unusual risks for malignancies. A long-term follow-up study of a large number of patients (4,531) with chronic thyroiditis at the Noguchi Hospital in Ooita Prefecture was conducted for 0-24 years, the objective being to assess risks for various sites of neoplasms by comparing the observed numbers of deaths with the expected numbers computed from the mortality rates in Japan. There was no increase in risk for overall malignancies (90 observed vs. 104.1 expected) or breast cancer (4 observed vs. 5.7 expected). The patients had an increased risk for myelo- and lympho-proliferative neoplasms (13 observed vs. 4.9 expected, P less than 0.01), as found in a few previous follow-up studies. A new and unexpected finding was that the patients showed decreased risk for cancers of digestive tract (24 observed vs. 44.3 expected, P less than 0.01). The reason for this decline could not be elucidated in this study, so that further epidemiological studies and animal experiments in this respect are needed.