Keloids are benign but can significantly affect patient quality of life. Since surgical resection alone associates with recurrence rates of up to 50–80% [1, 2], resection followed by postoperative radiotherapy has become the standard treatment for these scars over the last few decades. This treatment paradigm is supported by the fact that the risk of carcinogenesis from keloid radiotherapy appears to be very low: our PubMed literature search showed that over the last 70 years, only six cases of putative keloid radiotherapy-induced carcinogenesis have been reported. The tumors were fibrosarcoma, basal-cell carcinoma, thyroid carcinoma, breast-ductal carcinoma (two cases), and mucoepidermoid carcinoma. Five of these cases were summarized in a 2009 review [3] while the mucoepidermoid-carcinoma case was reported in 2012 [4]. The radiation doses ranged from 10.5 to 80 Gy. Three patients were children (9–13 years old) at the time of treatment. Most tumors took at least 8 years to develop. However, three cases cannot be definitively declared to be radiation-induced carcinomas. One was the fibrosarcoma case, which rose unusually quickly after radiotherapy (3.5 years). Moreover, the two breast-carcinoma cases had relevant family history and a history of oral hormone therapy, respectively. Thus, carcinogenesis after keloid radiotherapy is vanishingly rare and is likely to be even rarer with current keloid-treatment regimens, which carefully apply radiation at moderate doses of 8–25 Gy and stringently avoid treating children [5].
Radiation-induced sarcomas were defined by Cahan et al. in 1948 [5]; the definition was then modified by Arlen et al. in 1971 [6]. Thus, a tumor is considered to be a radiation-induced sarcoma if (i) its histology differs from that the primary tumor that required radiotherapy, (ii) it lies within the therapeutic irradiation area, and (iii) the duration between radiotherapy and tumor detection is relatively long. Our case meets all of these criteria and thus appears to be the first reported case of keloid radiotherapy-induced extraskeletal osteosarcoma.
In our case, the radiotherapy dose was 32 Gy, which is greater than current keloid-radiotherapy doses. Thus, the risk of extraskeletal osteosarcoma after this therapy is very low. Nevertheless, this case indicates that we should be aware that radiation therapy for keloids does carry a risk of carcinogenesis. Patients with keloids should be told of this risk and advised that long-term follow-up will be required if they undergo keloid resection followed by radiotherapy.