Radiation-induced sarcoma

Radiation-induced
fibrosarcoma after breast-conserving therapy for breast cancer: a case report and literature review. Ultrasonography and magnetic resonance imaging of the tumor. Ultrasonography scans revealed a 21.3-mm tumor in breast (a). Magnetic resonance imaging revealed 16 mm irregular geometries close to the skin (b)
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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. Malignant fibrous histiocytoma and osteosarcoma are the two most common histological types.

Epidemiology

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

It was found a higher risk of RIS among younger patients; it has been through a link between a particular cancer type that is more common among the young . There is a direct correlation with the risk and the radiation doses .

Clinical presentation

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

Pathology

Malignant fibrous histiocytoma 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 :

  • 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

Treatment and prognosis 

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

Similar to primary sarcomas, RIS originating soft-tissues has on tumor size and grade the two most important prognostic factors :

  • 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

RIS originating in bone is usually approached with primary chemotherapy followed by a margin-negative excision .

History and etymology 

RIS was first described in the 1920s in workers painting radium watch dials .