Molecular analysis of clonality of sporadic angiomyolipoma

Angiomyolipoma, which consists of three intimately intermixed components, smooth muscle, blood vessels, and adipose tissue, is variably considered a hamartoma, a choristoma or a true neoplasm. This study has investigated the clonality of sporadic angiomyolipomas in seven women, each with a single lesion, by determining the pattern of X-chromosome inactivation. Polymerase chain reaction (PCR) amplification of the highly polymorphic human androgen receptor gene (HUMARA) was performed on the DNA extracted from the paraffin-embedded lesional tissue microdissected to sample the admixed smooth muscle and blood vessel component (SMC/BV) and the adipose tissue component. All seven patients were heterozygous for HUMARA polymorphism upon amplification of undigested DNA from non-lesional tissue and were therefore informative for further analysis. In all patients, lesional DNA, representative of the components, was predigested with HpaII restriction enzyme for amplification of the methylated allele. In six patients, the lesions were clonal, while in one, polyclonal. The polyclonal lesion was small and had less than 20 per cent SMC/BV component. Microdissected SMC/BV component was clonal in 6/7 lesions; the scanty SMC/BV in the remaining lesion did not yield amplifiable DNA. Microdissected adipose tissue was polyclonal in all seven lesions. Angiomyolipomas are three clonal lesions due to a clonal smooth muscle cell and blood vessel component, while the polyclonal adipose tissue is probably metaplastic or reactive.