Loss of heterozygosity at the FLCN locus in early renal cystic lesions in dogs with renal cystadenocarcinoma and nodular dermatofibrosis.

Small, macroscopically visible cysts on the surface of the kidneys were observed in eight 6-8-week-old puppies diagnosed with renal cystadenocarcinoma and nodular dermatofibrosis (RCND). Histologic examination of the renal cortices in these puppies reveals numerous small cystic tubular changes. Hyperplastic change of the epithelial lining of cysts is frequently observed. By laser-capture microdissection we have sampled epithelial cells from such early renal cystic lesions in eight paternal half-sibs diagnosed with RCND. DNA was obtained from the laser-captured material, and all coding exons of the germline-mutated FLCN gene were sequenced to detect putative second hits. Samples from 31 independent hyperplastic epithelial cell sections of tubular microcysts of the RCND siblings were examined as well as normal control samples of the tissue sections. Loss of heterozygosity was detected in 35% of the transformed samples. The frequently observed loss of heterozygosity at the FLCN locus in atypical epithelial cells lining the cysts suggests that loss of heterozygosity/function of the FLCN gene may contribute to neoplastic transformation of renal epithelial cells at a very early age of RCND-affected dogs. The transformed renal epithelial cells seem to grow slowly in young puppies, which indicates that other mutational events are required for the development of tumors in adult dogs.