A case of collision tumor in the left maxillary sinus composed of adenoid cystic carcinoma (ACC) and metastatic hepatocellular carcinoma (HCC) is reported. Radiographic examination revealed masses in the liver and bilateral lung metastases. Histologically, proliferation of tumor cells with resemblance to HCC was observed, in addition to the ACC. For this reason, differential diagnosis between a second primary tumor and metastasis was made. The metastatic lesion immunohistochemically showed positivity for hepatocyte antigen (OCH1E5) and protein induced by vitamin K absence or antagonist II (PIVKA-II), sustaining the HCC diagnosis. Primary ACC and metastatic HCC in the maxillary sinus are rare, and this may therefore be the first case of maxillary sinus tumor with both these elements.

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