Carcinoma ex pleomorphic adenoma (Ca ex PA) is a carcinoma arising from a primary or recurrent benign pleomorphic adenoma. In this report, we present a case of a minimally invasive Ca ex PA arising in the submandibular gland. The patient was a 62-year-old man with a chief complaint of pain in the right submandibular region. The clinical diagnosis was a benign tumor in the submandibular gland and surgical resection was performed. The tumor contained a small amount of tumor-cell components, and showed a malignant area and a benign area. The malignant area was poorly differentiated adenocarcinoma, immunohistochemically the tumor cells were positive for HER2, and the Ki-67 labeling index was about 60%. The extent of capsular invasion was 1.4 mm into the adjacent tissues. The benign area was pleomorphic adenoma, negative for HER2, and the Ki-67 labeling index was about 4%. The diagnosis was Ca ex PA, minimally invasive type, although there were nerve and vascular invasions and poor prognostic factors, such as positivity for HER2 and high-grade malignancy components. We performed post-operative radiotherapy. Careful clinical follow-up is necessary.
