VHL mosaicism: the added value of multi-tissue analysis

Abstract

Von Hippel-Lindau disease (VHL) is an autosomal dominant, inherited syndrome with variants in the VHL gene causing predisposition to multi-organ benign and malignant neoplasms. A germline VHL variant is identified in 95-100% of individuals with a clinical diagnosis of VHL. Here, we present the case of an individual with a clinical diagnosis of VHL disease where peripheral blood DNA analysis did not detect a VHL variant. Sequencing of four tumor tissues (ccRCC, pheochromocytoma, lung via sputum, liver) revealed a VHL c.593 T > C (p.Leu198Pro) variant at varying allele fractions (range: 10-55%) in all tissues. Re-examination of the peripheral blood sequencing data identified this variant at 6% allele fraction. Tumor analysis revealed characteristic cytomorphological, immunohistochemical reactivity for alpha-inhibin, and CAIX, and reduced pVHL reactivity supported VHL-related pseudohypoxia. This report of a rare case of VHL mosaicism highlights the value of tissue testing in VHL variant negative cases.

Fig. 1. Morphological and immunohistochemical findings of pheochromocytoma.

Whole scanned images: The adrenalectomy specimen (hematoxylin and eosin) shows an encapsulated pheochromocytoma with clear cell change, variable fibrohyaline, and myxoid stroma rich in microvasculature (a, b). The tumor cells are diffusely positive for tyrosine hydroxylase (the rate limiting enzyme in catecholamine synthesis) (c). The tumor is positive for carbonic anhydrase IX (d). Alpha-inhibin shows variable weak reactivity in the tumor cells (e). pVHL shows variable loss or significantly reduced staining intensity in the tumor cells (f).

Fig. 2. Visualization of VHL variant in tumor and germline DNA.

Integrative Genomics Viewer display of the c.593 T > C (p.Leu198Pro) variant in tissue from four tumor specimens (a) and peripheral blood leukocytes (b). The percentage of sequencing reads (gray bars) depicting the variant are beside the biospecimen type. The blue bars depict a cytosine nucleotide instead of a thymine nucleotide at the variant loci. The overall proportion of cytosine:thymine reads is represented by the blue:red bars at the top of each tissue panel. Tumor cellularity was estimated by a pathologist to be 65% in the kidney tissue and 85% in the adrenal gland, lung, and liver tissue.