Adenoid cystic carcinoma (ACC) is one of the most common salivary gland malignancies. In rare cases, ACC undergoes high-grade transformation, which is associated with poor prognosis, in contrast to relatively long survival in the conventional ACC. Conventional ACC is characterized by typical histopathology showing glandular arrangement with sharply demarcated lumina, the tumor cells have sparse cytoplasm and angulated hyperchromatic nuclei. ACCs undergoing high-grade transformation lack these morphological features. In this paper we present a case of 46 years old female patient presenting with locally advanced tumor of the parotid gland and neck lymphadenopathy, coming for surgery. A suspect lymph node was sent to freeze section histology. Large non-cohesive cells with vesicular nuclei and prominent nucleoli along with well persevered lymph node architecture were seen in the frozen slide. This finding lead to suspicion of a lymphoma, the surgery finished in the extent of superficial parotidectomy and selective neck dissection of regions II-IV. Subsequent histopathological examination of formalin-fixed lymph node proofed epithelial nature of the atypical cells by p63 positivity. In the parotid gland resection specimen, an ACC with high-grade component was indentified. The high-grade ACC shared cell morphology with the lymph node metastasis. 17 from 20 lymph neck nodes contained metastases of high-grade ACC. Interestingly, there was strong CD117 expression in the high-grade ACC, whereas the conventional part was fully negative. To the best of our knowledge, the high-grade ACC of the parotid gland was reported only in 10 cases in the medical literature.
Keywords: adenoid cystic carcinoma; high grade; metastatis; parotid gland; transformation.