[Clinicopathological analysis of adult hepatic mesenchymal hamartoma]

Objective: To explore the clinicopathological and molecular genetic features of adult hepatic mesenchymal hamartoma (MHL). Methods: A total of five confirmed adult MHL cases diagnosed at the Pathology Department of the First Medical Center of the People's Liberation Army General Hospital between 2009 and 2022 were collected. Histomorphological observation and immunohistochemical staining were conducted. Gene detection was performed by next-generation sequencing. Results: Among the five cases, four were male and one was female, aged 46-67 years, with an average age of 56.2 years. The maximum diameter was 5.3-13.5cm, and the average diameter was 9.2cm. Tumors were generally cystic, solid, or mixed cystic-solid. Histopathologically, in four out of five cases of MHL, malignant transformation occurred, of which three cases were malignantly transformed into undifferentiated embryonal sarcoma and one case was malignantly transformed into a malignant solitary fibrous tumor. NAB2-STAT6 gene rearrangements were identified. Conclusion: Adult MHL is a rare kind of tumor with malignant potential, and it is difficult to diagnose with preoperative imaging examinations. A fine-needle biopsy is rarely used for diagnosis, but surgical resection of symptomatic or enlarged lesions is recommended to rule out the possibility of malignancy and further diagnosis. Genetic testing results revealed the complex genetic alterations in MHL, and it was found that adult MHL can malignantly transform into malignant solitary fibrous tumors. We believe that genome-wide analysis is necessary to determine the unique molecular characteristics of MHL and identify potential targets for therapeutic intervention.