Risk factors for subsequent thyroid neoplasms development in childhood cancer survivors.

Subsequent thyroid carcinomas (STC) are common after childhood cancer treatment and have well-described risk factors, whereas information on subsequent thyroid adenomas (STA) remains limited. This study compared treatment-related risk factors for STC and STA, assessed their associations with the other subsequent neoplasms and evaluated the incidence of STC relative to the age-matched national general population. The study cohort included 4348 childhood cancer survivors treated between 1975 and 2020; 48% were female, 23% had lymphomas and 77% had solid tumors. STC occurred in 44 survivors (59% female) and STA in 23 (65% female). Compared with the national general population, the risk of STC was 7.6-fold higher in females and 23.6-fold higher in males. The median age at diagnosis was lower for STC (25.8 vs. 29.8 years). Hodgkin lymphoma was the most frequent primary cancer (48% vs. 57%). The median age at first cancer diagnosis was similar (9.8 vs. 9.4 years). Neck radiotherapy was a major risk factor in both groups (59% vs. 83%). Additional subsequent malignant neoplasms occurred in 14% of STC patients and 13% of STA patients, while subsequent benign neoplasms occurred in 20% and 26%, respectively. The incidence of subsequent benign neoplasms was higher in STC patients compared to other first subsequent malignant neoplasm patients (p<0.05). STC predominated over STA (66%). Shared risk factors included neck radiotherapy and Hodgkin lymphoma. STC was diagnosed at a younger age. The frequent occurrence of additional subsequent neoplasms highlights the need for long-term surveillance.