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

Background. Mesenchymal hamartoma of the liver is a rare lesion seen p redominantly in childhood, which is believed to be either a developmen tal 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 relations hip between mesenchymal hamartoma and undifferentiated (embryonal) sar coma of the liver, some have speculated that mesenchymal hamartoma may be a neoplastic lesion with uncertain malignant potential. Methods. B ecause DNA aneuploidy can be useful as a marker for neoplasia, the aut hors decided to assess ploidy in paraffin embedded mesenchymal hamarto mas using flow cytometry. The authors retrospectively examined mesench ymal hamartomas from eight children and evaluated the clinicopathologi c features and the ploidy of the lesions. Results. Boys and girls were equally affected, and the mean age at presentation was 11 months. Les ions 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 w eights for three of the largest lesions were not recorded). Flow cytom etric analysis of nuclei extracted from paraffin embedded tissue revea led that six of the eight lesions were DNA diploid, whereas two were D NA aneuploid (with DNA indices of 1.13 and 1.25). All of the lesions h ad a low S phase fraction. Conclusions. The authors concluded that alt hough most mesenchymal hamartomas are diploid, a subset of mesenchymal hamartomas is aneuploid. The finding of aneuploidy in mesenchymal ham artoma, in conjunction with the reported cytogenetic abnormalities, su ggests that mesenchymal hamartoma may be a true neoplasm and not a dev elopmental anomaly or reactive process.