Abstract
Sarcoma caused by radiation therapy is called radiation-induced sarcoma (RIS). This rare pathology is being encountered with increasing frequency due to the longer survival time of patients after radiation therapy. We report a case of RIS in the anterior neck of an 82-year-old man who had achieved complete response from radiation therapy for subglottic cancer 11 years earlier. He presented to our facility with an enlarged anterior cervical tumor. Contrast-enhanced computed tomography (CT) indicated a massive tumor (27×34 × 45 mm) extending from the thyroid cartilage into the hyoid bone. Additional magnetic resonance imaging (MRI) showed a signal-hyperintense mass on T1-weighted imaging and signal heterogeneity on T2-weighted imaging, and contrast-enhanced MRI showed some enhancing effects in the tumor. Considering his history of radiation therapy and these imaging characteristics, RIS was suspected and complete resection of the tumor was performed. Dedifferentiated liposarcoma was diagnosed on histopathological examination. He has been followed-up for 6 months with no apparent recurrence.
Introduction
Radiation-induced sarcoma (RIS) is a rare tumor, with an incidence of 3.2 per 1000 patients of radiation therapy [ ]. The frequency of this tumor has recently been increasing, presumably due to the longer survival time of patients after radiation therapy.
Perthes first reported radiation therapy causing sarcoma in 1904 [ ]. Generally, RIS can develop about 10 years after radiation therapy anywhere in the body, but is relatively less common in the head and neck. Computed tomography (CT), magnetic resonance imaging (MRI), and pathological examination are performed, but RIS shows various histological types, and no typical imaging findings have been characterized. Liposarcoma is a rare subtype of RIS and is not well documented in the literature.
In this case, considering the history of radiation therapy and imaging findings of the patient, we suspected RIS and completely resected the tumor. Histopathology confirmed dedifferentiated liposarcoma.
We report herein a case of radiation-induced liposarcoma of the head and neck.
Case presentation
An 82-year-old man had undergone radiation therapy 11 years earlier for subglottic cancer (T1N0M0), receiving a total dose of 70 Gy and obtained complete response. Eleven years after that initial treatment, he presented to our facility with a 2-month history of tumor in the anterior neck. He drank 350 ml of beer and a little shochu every day, but had no medical history aside from the subglottic cancer, and was an ex-smoker. Contrast-enhanced CT indicated a massive tumor extending from the thyroid cartilage into the hyoid bone, measuring 27×34 × 45 mm and showing a contrast effect ( Fig. 1 ). MRI showed that the tumor had not invaded into the thyroid cartilage ( Fig. 2 ). Pre-operative histopathological examination revealed spindle cells with positive immunostaining for CDK4. We strongly suspected RIS and performed complete resection of the tumor. We tried to preserve the larynx as much as possible, in accordance with the wishes of the patient. The tumor had not invaded the thyroid cartilage and the perichondrium was therefore resected as a safety margin to preserve the thyroid cartilage ( Fig. 3 A). The inside of the tumor was white and highly cellular ( Fig. 3 B). Postoperative histopathological examination revealed spindle cell proliferation with some desmoplastic changes. Immunostaining showed positive results for CDK4 and scattered positivity for MDM2 ( Fig. 4 ). We diagnosed dedifferentiated liposarcoma. As of the time of writing, 6 months postoperatively, no signs of recurrence have been identified.
Discussion
A diagnosis of RIS requires each of the following: i) a patient who received radiation therapy more than 3 years ago; ii) sarcoma appearing in the area that had received radiation therapy; and iii) sarcoma of a tissue type differing from that of the primary tumor [ ].
A latency period is necessary to differentiate RIS from sporadic sarcoma, but has remained controversial over the years. No specific histopathological criteria exist for RIS [ ]. RIS is a rare tumor, occurring in the whole body with an incidence of 0.32%, and in the head and neck with an incidence of 0.06–0.17% [ ]. Survival rates of patients who have received radiation therapy have kept improving over the years, and the incidence of RIS has thus increased [ ]. The mean latency period is 11 years, depending on the tissue type, with liposarcoma showing the shortest latency and leiomyosarcoma the longest [ ]. Risk factors include young age at treatment, high dose of radiation, and chemotherapy using alkylating agents [ , ]. The 5-year survival rate is 17–58%, shorter than those of other sarcomas. 6 The prognosis is worst for malignant peripheral nerve sheath tumor (MPNST), a malignant fibrous histiocytoma, with a 5-year survival rate of 12% [ ]. Conversely, the prognosis for fibrosarcoma is best, with a 5-year survival rate of 76% [ ].
MPNST is the most common tissue type of RIS, followed by angiosarcoma, leiomyosarcoma, and fibrosarcoma [ ]. Radiation-induced liposarcoma appears to be the rarest type, with our search of the literature yielding 6 cases [ ]. Patient characteristics in these 6 cases are summarized in Table 1 . Age at RIS diagnosis ranged from 16 to 86 years, with an interval between radiation exposure and development of sarcoma of 6–12 years. Patients with radiation-induced liposarcoma underwent surgery or received chemotherapy or radiation therapy.
