The patient underwent a panendoscopy and a cT3 cN2b oral cavity carcinoma on the right side was histologically confirmed as the most likely secondary malignancy in a case of tongue margin carcinoma on the left with primary surgical treatment and adjuvant interstitial brachytherapy. The surgical procedure was recommended in our interdisciplinary tumor conference. Computed tomography showed an extensive mass in the area of the right floor of the mouth and the edge of the tongue with infiltration of the base of the tongue and almost per continuitatem growth towards the neck metastasis. In addition, contact with the mandibular branch without clear signs of infiltration. Rapid clinical progression of the tumor.