The most appropriate treatment is resection. This 42-year-old woman has a large hepatocellular adenoma, which has been confirmed by biopsy of the mass, and β-catenin activation mutation is positive. Hepatic adenomas can be subclassified based on genotype or immunohistochemistry, which provides information about the risk of transformation to hepatocellular carcinoma (HCC). Hepatic adenomas with positive genotyping for β-catenin activation or that are positive for the correlating immunohistochemistry study for glutamine synthetase have a higher risk of transformation to liver cancer. It is generally best to resect hepatic adenomas that are larger than 5 cm, arise in males (because they carry a higher risk of transformation to HCC), exhibit hemorrhage, or are positive for β-catenin activation/glutamine synthetase antibody. Low-risk hepatocellular adenomas are those smaller than 5 cm that arise in young women on oral contraceptives (reversible cause), as well as steatotic hepatocellular adenomas that are positive for the HNF-1α inactivation mutation. These low-risk hepatocellular adenomas require CT imaging surveillance at 6- to 12-month intervals.

Oral contraceptives are associated with the development and growth of hepatocellular adenomas, and cessation of oral contraceptives may lead to shrinkage and/or resolution. However, stopping oral contraceptives is not by itself sufficient treatment for this patient because her hepatic adenoma is larger than 5 cm and is β-catenin positive.

CT imaging surveillance is not appropriate given the high-risk characteristics of this patient's adenoma.

Transarterial chemoembolization is not an established treatment modality for hepatocellular adenomas. This therapy may be appropriate in a patient with cirrhosis and large or multiple hepatocellular carcinoma lesions that are unresectable.