Radiation-induced sarcoma

Last revised by Joshua Yap on 15 Oct 2022

Radiation-induced sarcoma (RIS) can originate in either the irradiated bone or soft tissues after a period of latency. They are usually high-grade tumors with a poor prognosis when compared with primary sarcomas. Undifferentiated pleomorphic sarcoma and osteosarcoma are the two most common histological types. 

The incidence is not well known as it is related theoretically to all radiation therapy procedures 1. One study in Finland taking into consideration all treated parts of the body found a risk of 0.05% 2. Radiation-induced sarcoma constitutes ~4% of all sarcomas 3.

The study also found a higher risk of radiation-induced sarcoma among younger patients through a link between a particular cancer type that is more common among the young 2. There is a direct correlation with the risk and the radiation doses 4.

A history of prior radiation therapy is mandatory for a diagnosis of radiation-induced sarcoma to be made. The median latency period is around 14 years 4, however, radiation-induced sarcoma can develop in a short time as 3-4 years following radiotherapy. 

Undifferentiated pleomorphic sarcoma and osteosarcoma are the two most common histological types, although other histologies (e.g. angiosarcoma and rhabdomyosarcoma) can occur. 

The following criteria have been proposed to determine a sarcoma as radiation-induced 5,6

  • history of radiation therapy: the sarcoma should arise within an area included in the radiation portal

  • no history of sarcomas before the radiation therapy

  • the sarcoma manifests after a latency period of at least 2 years after the radiation therapy

  • histologic confirmation of a sarcoma

Radiation-induced sarcoma has a poor prognosis compared to primary sarcomas: the 5-year-survival rates vary from 17-58% in radiation-induced sarcoma compared with 54-76% in patients with sporadic sarcomas. Some unfavorable factors related to radiation-induced sarcomas are central tumor site, incomplete surgical remission, microscopic tumor necrosis, and the presence of metastases, the two former factors which are overrepresented in radiation-induced sarcoma 3.

Similar to primary sarcomas, tumor size and grade are the two most important prognostic factors 1:

  • high-grade tumors larger than 5 cm: usually treated with primary chemotherapy followed by a margin-negative surgical excision of the residual disease 

  • low-grade tumors and high-grade tumors with 5 cm or smaller: usually treated with a margin-negative surgical excision and systemic chemotherapy is considered when a negative margin is not certain

Radiation-induced sarcoma originating in bone is usually approached with primary chemotherapy followed by a margin-negative excision 1

Radiation-induced sarcoma was first described in the 1920s in workers painting radium watch dials 4.

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