ABSTRACT
Background: Exposure to ionizing radiation during childhood is a well-established risk factor for thyroid cancer. However, the genetic mechanisms of radiation-associated carcinogenesis remain not fully understood. Methods: In this study, we used targeted next-generation sequencing and RNA-Seq to study 65 papillary thyroid cancers (PTCs) from patients in the Ukrainian-American cohort with measurement-based iodine-131 (I-131) thyroid doses received as a result of the Chernobyl accident. We fitted linear regression models to evaluate differences in distribution of risk factors for PTC according to type of genetic alteration and logistic regression models to evaluate the I-131 dose response. All statistical tests were two-sided. Results: Driver mutations were identified in 96.9% of these thyroid cancers, including point mutations in 26.2% and gene fusions in 70.8% of cases. Novel driver fusions such as POR-BRAF, as well as STRN-ALK fusions that have not been implicated in radiation-associated cancer before, were found. The mean I-131 dose in cases with point mutations was 0.2 Gy (range = 0.013-1.05 Gy), statistically significantly lower than 1.4 Gy (range = 0.009-6.15 Gy) for cases with fusions (P < .001). No driver point mutations were found in tumors from individuals who received more than 1.1 Gy of radiation. Relative to tumors with point mutations, the proportion of tumors with gene fusions increased with radiation dose, reaching 87.8% among individuals exposed to 0.3 Gy or higher. With a limited study sample size, the estimated odds ratio at 1 Gy was 20.01 (95% confidence interval = 2.57 to 653.02, P < .001). In addition, after controlling for I-131 dose, we found higher odds ratios for gene fusion-positive PTCs associated with several specific demographic and geographic features. Conclusions: Our data provide support for a link between I-131 thyroid dose and generation of carcinogenic gene fusions, the predominant mechanism of thyroid cancer associated with radiation exposure from the Chernobyl accident.
Subject(s)
Chernobyl Nuclear Accident , Gene Fusion , Iodine Radioisotopes/adverse effects , Mutation , Neoplasms, Radiation-Induced/genetics , Oncogene Proteins, Fusion/genetics , Thyroid Neoplasms/genetics , Adolescent , Adult , Anaplastic Lymphoma Kinase/genetics , Biomarkers, Tumor/genetics , Calmodulin-Binding Proteins/genetics , Carcinoma, Papillary/etiology , Carcinoma, Papillary/genetics , Carcinoma, Papillary/pathology , Child , Child, Preschool , Cohort Studies , Cytochrome P-450 Enzyme System/genetics , Female , Follow-Up Studies , High-Throughput Nucleotide Sequencing , Humans , Infant , Male , Membrane Proteins/genetics , Neoplasms, Radiation-Induced/etiology , Neoplasms, Radiation-Induced/pathology , Nerve Tissue Proteins/genetics , Prognosis , Proto-Oncogene Proteins B-raf/genetics , Radiation Dosage , Thyroid Neoplasms/etiology , Thyroid Neoplasms/pathology , Young AdultABSTRACT
A 77-year-old white male presented to the clinic with two isolated cutaneous tumors on his forehead. A cutaneous biopsy showed a focally folliculotropic CD4 cutaneous lymphoma. The tumors were irradiated with a complete response, and he was started on oral bexarotene. He experienced localized cutaneous relapse 3 months into treatment. These new tumors now revealed a surprisingly CD8 cytotoxic phenotype, but with the same clone. A systemic workup was negative. His regimen was switched to romidepsin, and he was treated with local radiation again. Another 3.5 months passed in remission until he developed widespread cutaneous tumors. Positron emission tomography/computed tomography revealed multifocal systemic disease involving his diaphragm, liver, distal duodenum, proximal jejunum, anterior chest wall including pectoral muscles, and lungs without significant adenopathy. He died a few days later. Given his full clinical and pathological course, he was given the diagnosis of an aggressive primary cutaneous T-cell lymphoma, unspecified.