Primary mucoepidermoid carcinoma of the liver: Clinicopathological features, molecular changes and prognosis.

Primary mucoepidermoid carcinoma of the liver (MEC-L) is an exceptionally rare malignant tumor characterized by mucinous, epidermoid, and intermediate cells, resembling its salivary gland counterpart. To date, only 24 cases of MEC-L have been reported in the English literature. We present two additional MEC-L cases diagnosed at the Third Affiliated Hospital of Sun Yat-sen University from January 2023 to May 2025, along with a review of 24 published cases. Clinical data, laboratory results, pathological findings, and follow-up information were collected. Thirty-three cases of conventional cholangiocarcinoma (CCA) were included for comparison. Next-generation sequencing (NGS) was performed for all cases. The median age of MEC-L patients was 64 years (range: 35-81 years), with a male-to-female ratio of 16:10, and a median tumor size of 8 cm. MEC-L displayed non-specific clinical and radiological features, with pathology similar to MECs arising in other anatomical sites. Only 16.67% (1/6) of MEC-L cases showed MAML2 rearrangement. Mutations in TP53, CDKN2A and CDKN2B were identified in one case, and mutations in KRAS, PIK3CA, CDK4, MDM2 and MYC were found in another case. The clinicopathological features and mutational profiles of MEC-L closely resembled conventional CCA, but MEC-L had a significantly poorer overall survival (p < 0.05). Age and tumor type were independent prognostic factors for CCA, but no distinct clinicopathological factors were identified for MEC-L. In conclusion, MEC-L is a rare subtype of CCA, who shows similar clinicopathological features and mutational profiles with conventional CCA except for poor prognosis.