Background: Hepatobiliary mucinous cystic neoplasms (MCN) harbor an invasive carcinoma in 16% of the cases, mainly tubular type, but occasionally sarcomatoid or undifferentiated, these entities being frankly rare.
Methods: We present the case of a liver MCN with an invasive component and sarcomatous degeneration.
Results: The patient was treated surgically with subsequent adjuvant chemotherapy (capecitabine), presenting tumor progression after three months with peritoneal carcinomatosis and liver recurrence. The patient died due to liver failure 4 months after surgery.
Conclusion: MCN with an invasive component and sarcomatous degeneration are very rare, present advanced stages, show aggressive behavior, and have a poor prognosis.
Keywords: Mucinous cystic liver neoplasm; Pancreatic cystic neoplasm; liver surgery; sarcomatous differentiation.