Unusual second malignancies following radiation therapy: subcutaneous pleomorphic rhabdomyosarcoma and cutaneous melanoma. Two case reports.

Background: Among nonepithelial second neoplasms which are known to be induced by irradiation, rhabdomyosarcomas are extremely rare, and melanomas are infrequent. We report a high-grade sarcoma with rhabdomyoblastic differentiation, which appeared 30 years after megavoltage irradiation for an endometrial adenocarcinoma, and a malignant melanoma which arose after 6 years in the irradiation field of a fibrosarcoma.
Methods: Histology and immunohistochemistry were performed in both cases. In the first case, electron microscopy was also performed. In the second, the previous tumor was re-evaluated.
Results: The first case showed histological, immunohistochemical and ultrastructural features of a rhabdomyosarcoma. In the second case, a lentigoid malignant melanoma was histologically and immunohistochemically demonstrated, whereas the previously resected tumor was a fibrosarcoma negative to melanoma markers.
Conclusions: Rare cases of rhabdomyosarcomas and melanomas are induced by irradiation, although in some cases other factors (i.e., genetic risk, chemotherapy) may have a prominent etiopathogenetic role in their development. A close follow-up and a careful examination of the irradiated area should facilitate an early diagnosis of these aggressive postradiation second neoplasms.