Prevalence of latent thyroid cancer in forensic autopsy cases from Fukushima Prefecture and a distant region: A histopathological study in Japan

Latent thyroid carcinoma is frequently identified as an incidental microscopic malignancy in autopsy studies, providing valuable insight into the baseline occurrence of thyroid carcinoma, independent of clinical detection patterns. This study compared the prevalence of latent thyroid carcinoma in forensic autopsy cases from Fukushima Prefecture, an area affected by the 2011 nuclear accident, with that of forensic autopsy cases from Ishikawa Prefecture, a geographically distant and non-exposed region. Thyroid glands from 1,102 autopsies in Fukushima (2013–2023) and 310 autopsies in Ishikawa (2016–2023) were examined using uniform histopathologic methods. Latent thyroid carcinoma was defined as clinically undiagnosed thyroid carcinoma first detected at autopsy. Overall, 85 cases (7.7%) were identified in Fukushima and 37 cases (11.9%) in Ishikawa, representing a significantly higher prevalence in Ishikawa (odds ratio 1.62, p = 0.020). This result was consistent after age (odds ratio 1.53, p = 0.047) and sex (odds ratio 1.59, p = 0.029) adjustment, as well as after adjustment for both age and sex simultaneously (odds ratio 1.56, p = 0.041). No latent thyroid carcinoma was detected among individuals younger than 20 years in either region. Although we did not directly investigate whether radiation exposure influenced latent thyroid carcinoma prevalence, the study’s findings do not indicate an increased prevalence of latent thyroid carcinoma in Fukushima, despite the nuclear accident. These autopsy-derived estimates provide an important epidemiologic baseline for interpreting thyroid carcinoma surveillance data and underscore the value of pathological assessments in post-disaster health monitoring.