Radiation-induced carcinosarcoma of the submandibular gland: case report and review of literature. Radiation-induced carcinosarcoma (RICS) of the head and neck is a very rare and extremely aggressive entity. We present the case of a 60-year-old man diagnosed with a T2N2cM0 squamous cell carcinoma at the right base of the tongue (BOT). The patient was treated with neoadjuvant chemotherapy and 3D-conformal radiotherapy (3D-CRT) to the BOT and bilateral neck. He developed left submandibular firmness five years after treatment, initially diagnosed as radiation-induced fibrosis. The increasing size of the left submandibular mass two years later prompted further imaging, which showed a 2.2x1.8 cm mass in the left submandibular region in the previously irradiated field. This was diagnosed as a radiation-induced submandibular gland malignancy. This is the first reported case of a RICS in the submandibular gland and demonstrates the importance of early workup and evaluation of submandibular gland pathology in a patient with a history of radiation for a head and neck malignancy.