Primary mucoepidermoid carcinoma of the liver with CRTC1-MAML2 fusion: a case report

CRTC1-MAML2 fusion is often detected in low- or intermediate-grade salivary mucoepidermoid carcinoma (MEC), and it is associated with a favorable clinical course. Primary MEC of the liver is an extremely rare, aggressive tumor, and no study has investigated CRTC1-MAML2 fusion. A 79-year-old Japanese female presented with an approx. 5-cm hepatic mass lesion. We surgically resected the lesion under the clinical diagnosis of intrahepatic cholangiocarcinoma. The histological and immunohistochemical findings were consistent with high-grade MEC, consisting of squamoid, mucin-producing, and intermediate tumor cells. Our RT-PCR analysis revealed the presence of CRTC1-MAML2 fusion. This fusion gene was further confirmed by direct sequencing. The patient is still alive almost 10 years after the surgery. This is the first case report of primary MEC of the liver with CRTC1-MAML2 fusion, with long survival. The present case has significant implications for the entity of primary MEC of the liver which should be distinguished from adenosquamous carcinoma.