Chromosomal analysis of renal angiomyolipoma by comparative genomic hybridization: evidence for clonal origin

Angiomyolipoma has long been considered a hamartomatous polyclonal proliferation. However, recent molecular analyses have indicated that these tumors may be clonal neoplasms rather than polyclonal proliferations. We investigated chromosomal imbalances in angiomyolipoma by comparative genomic hybridization. DNA was extracted from archival paraffin-embedded and frozen tissues of 12 angiomyolipomas (10 usual variant, two epithelioid variant). The 10 angiomyolipomas of the usual variant included bilateral tumors from one tuberous sclerosis patient. Fluorescence ratio distributions from tumor hybridizations were compared with those from control hybridizations to detect changes in DNA copy number with high sensitivity and specificity. We identified 20 chromosomal imbalances in seven sporadic angiomyolipomas, including both tumors of the epithelioid variant. The remaining five tumors, including the two angiomyolipomas from a tuberous sclerosis patient, were devoid of chromosomal imbalances. Seventy-five percent of the imbalances were partial or whole chromosomal deletions involving disparate genomic regions, some of which have previously been associated with tumors of adipose tissue and smooth muscle tumors. Four angiomyolipomas of the usual variant showed 5q deletions with a common region of deletion spanning 5q33 to q34. In two tumors, deletion on 5q was the sole abnormality. One epithelioid angiomyolipoma showed 5q gain encompassing the same region in addition to other alterations. We concluded that (1) Chromosomal imbalances are common in renal angiomyolipomas; (2) Presence of clonal genomic alterations lends further support to the neoplastic pathogenesis of these tumors; (3) The 5q33-q34 region may contain a tumor suppressor gene significant in the histogenesis of some renal angiomyolipomas.