Young Adult Secondary Cancer After Proton Beam Therapy: A Case Study

Proton beam therapy (PBT) is a crucial radiotherapy treatment method for pediatric cancers. It can significantly reduce the long-term side effects of radiation by limiting the exposure to areas outside the planned irradiated field. However, the risk of developing radiation-related secondary cancers remains, although its incidence rate is lower than that of photon beam therapy. In this study, we report the first young adult patient in Japan who developed a secondary cancer from the irradiated field after PBT for Ewing's sarcoma. Thereafter, the patient underwent cancer genome profiling (CGP) test.The patient was diagnosed with Ewing's sarcoma with EWS-Fli1 translocation at 14 years of age. The tumor was found adhering to the left lung in the left thoracic cavity. Remission was achieved with intensive chemotherapy, autological hematopoietic stem cell transplantation, and PBT; eight years later, he developed anaplastic pleomorphic sarcoma in the irradiated field. He underwent CGP test (the FoundationOne CDx Cancer Genomic Profile), which did not find any drug target variants. Fortunately, ifosfamide, carboplatin, and etoposide (ICE) therapy effectively controlled the disease for more than six months.Controlling secondary cancers is important during pediatric, adolescent, and young adult cancer treatment. There are few reports available on CGP testing using secondary cancer specimens from pediatric, adolescent, and young adult cancer patients. Therefore, it is desirable to have accurate epidemiological studies on secondary cancer development within the irradiated field after PBT and gene analysis about the mechanism of secondary cancers carried out in the large cohort. (245 words)