MESENCHYMAL HAMARTOMA OF THE LIVER - DNA FLOW CYTOMETRIC ANALYSIS OF 8 CASES

Background. Mesenchymal hamartoma of the liver is a rare lesion seen predominantly in childhood, which is believed to be either a developmental anomaly or reactive process. Because of recent reports of specific translocations involving chromosome 19 in mesenchymal hamartomas and certain ultrastructural and histologic features suggesting a relationship between mesenchymal hamartoma and undifferentiated (embryonal) sarcoma of the liver, some have speculated that mesenchymal hamartoma may be a neoplastic lesion with uncertain malignant potential. Methods. Because DNA aneuploidy can be useful as a marker for neoplasia, the authors decided to assess ploidy in paraffin embedded mesenchymal hamartomas using flow cytometry. The authors retrospectively examined mesenchymal hamartomas from eight children and evaluated the clinicopathologic features and the ploidy of the lesions. Results. Boys and girls were equally affected, and the mean age at presentation was 11 months. Lesions involved predominantly the right lobe of the liver, with a range of greatest dimension of 7-25 cm, and a mean weight of 651 g (though weights for three of the largest lesions were not recorded). Flow cytometric analysis of nuclei extracted from paraffin embedded tissue revealed that six of the eight lesions were DNA diploid, whereas two were DNA aneuploid (with DNA indices of 1.13 and 1.25). All of the lesions had a low S phase fraction. Conclusions. The authors concluded that although most mesenchymal hamartomas are diploid, a subset of mesenchymal hamartomas is aneuploid. The finding of aneuploidy in mesenchymal hamartoma, in conjunction with the reported cytogenetic abnormalities, suggests that mesenchymal hamartoma may be a true neoplasm and not a developmental anomaly or reactive process.