Abstract 133: Rewinding the tape of life: somatic profiling in Von Hippel-Lindau (VHL) disease reveals evolutionary contingency and constraints
Authors: Shepherd Scott T. , Coulton Alex , Vocke Cathy D. , Ricketts Chris J. , Ball Mark , Byrne Fiona , Dovga Yuliia , Fendler Annika , Taja Barber , O'Neill Olga , Gerontogianni Lina , Kelly Gavin , Schmidt Laura S. , Crooks Daniel R. , Choo Kirstin , Gautam Rabindra , Blake Zoe , Reynolds Krista , Litchfield Kevin , Merino Maria , Linehan Marston W. , Turajlic Samra 
Published: June 2023

Abstract
Whether cancer evolution follows a deterministic route prescribed by host factors (germline genetics and/or environment) or proceeds along multiple alternative trajectories due to the stochastic nature of evolution is unknown. Patients with VHL disease have a pathogenic germline mutation in VHL (3p25) and tumorigenesis occurs when the wild-type copy of VHL is lost. Patients develop multiple clonally independent tumors including clear cell renal cell carcinoma (ccRCC), pheochromocytoma or paraganglioma (PPGL) and pancreatic neuroendocrine tumors (pNET), offering an opportunity to test repeatability of evolutionary trajectories between and within patients.
We performed deep targeted exome sequencing, in 1520 tumors (993 solid ccRCC; 156 cystic ccRCC; 135 mixed solid/cystic ccRCC; 236 extra-renal) from 130 patients with VHL disease to evaluate somatic variants and copy number alterations, ploidy and chromosomal complexity. Tumor phenotype was evaluated from pathology reports and longitudinal growth kinetics from diagnostic MRI data. Analysis of 889 tumor samples is complete and profiling of the full cohort will be presented at the 2023 AACR meeting.
Within clonally independent tumors, we performed two tests to assess for evidence of convergence between tumors from the same patient. First, we tested for parallel events in canonical ccRCC drivers. We found significant enrichment of somatic VHL variants occurring in one patient with a germline whole VHL gene deletion encompassing neighboring BRK1. Contiguous BRK1 loss is associated with less aggressive ccRCC phenotype and our findings suggest a specific constraint in this patient. We next assessed for evidence of convergence by measuring the genetic distance of copy number and mutational profiles between and within patients with resampling and permutation. Similar somatic profiles between tumors were only detected in 1/76 patients whose tumors were characterized by infrequent somatic alterations beyond 3p loss indicating little evidence of convergence.
Cystic ccRCCs represent an indolent phenotype not associated with metastasis that may progress to solid tumors over time; we found mixed tumors closely resemble somatic profiles of solid tumors whereas cysts were characterized by infrequent copy number gains and low chromosomal complexity. We also identified cysts with specific losses (chr16, chr17, chr19p) mutually exclusive with 3p LOH suggestive of VHL-loss independent cyst formation. In solid ccRCCs, we found chromosomal complexity and loss of specific chromosomal loci (9p and/or 14q) are associated with diameter potentially reconciling the observation linking risk of metastasis to tumor diameter in VHL-related ccRCC.
In summary, within the constrained setting of VHL-related ccRCC, evolution is dominated by chance although specific patient and phenotype specific constraints are observed.
Citation Format: Scott T. Shepherd, Alex Coulton, Cathy D. Vocke, Chris J. Ricketts, Mark Ball, Fiona Byrne, Yuliia Dovga, Annika Fendler, Barber Taja, Olga O'Neill, Lina Gerontogianni, Gavin Kelly, Laura S. Schmidt, Daniel R. Crooks, Kirstin Choo, Rabindra Gautam, Zoe Blake, Krista Reynolds, Kevin Litchfield, Maria Merino, Marston W. Linehan, Samra Turajlic. Rewinding the tape of life: somatic profiling in Von Hippel-Lindau (VHL) disease reveals evolutionary contingency and constraints [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 133.