Synovial sarcoma of the lung in a patient who received radioactive iodine therapy for thyroid cancer

Background: Synovial sarcomas are uncommon malignancies that mainly affect adolescents and young adults. Most arise from the deep soft tissues of the extremities, but they can occur in other parts of the body such as the lung. Synovial sarcomas after radiation therapy are rare, in contrast with other sarcomas, with only 6 reported cases. Secondary malignancies after radioactive iodine (RAI) therapy are also uncommon, with the most consistent evidence for hematologic malignancies. Patient findings: We present what we believe to be the first report of a synovial sarcoma of the lung with an SS18/SSX1 translocation following RAI therapy. At age 20, the patient developed papillary thyroid cancer and later had two surgically confirmed recurrences. Over the course of her care she received a total of about 220 mCi of 131I. At age 34, as part of an evaluation for another suspected recurrence she had a PET/CT scan and a pulmonary mass was detected. Summary and Conclusion: Although not previously reported, this case suggests that synovial sarcomas may be a secondary malignancy following RAI therapy. The latency in this case is reasonable, the dose to the lungs was small, but in the range where radiation-related malignancy may occur, and the somatic chromosomal rearrangement could be a radiation effect.