Recurring urothelial carcinomas are clonal but incompatible with a direct relationship

Abstract

To describe the genetic relationship between the primary and recurrent bladder tumors and to identify their origins, different models such as the field cancerization, seeding, and intraepithelial migration have been proposed. The aim of this study was to investigate the genetic relationship in syn- and metachronous bladder tumors using different types of data, and to highlight supportive evidence for the proposed models. The exophytic part of primary and recurrence urothelial tumors were collected by cold-cup biopsy from patients undergoing transurethral resection at the Lund University Hospital, Sweden, between 2001 and 2007. In total, 49 tumors from 18 patients and their 18 matched normal samples obtained from peripheral blood were collected and hybridized on HumanCNV370-Duo Genotyping BeadChips (Illumina Inc.). Gene expression data were generated using Illumina HumanHT-12 Expression BeadChip. Tumors were classified according the Lund classification system. For 27 tumor samples and matched normal blood samples from 10 patients, a custom target captured panel was used to sequence 1697 cancer genes. We used the fact that patients with non-muscle invasive bladder tumors show frequent local recurrences and often have multiple tumors to study re-initiation of tumor growth from the same urothelium. By extensive genomic analyses we show that tumors from the same patient are clonal. We show that gross genomic chromosomal aberrations may be present then absent in a recurrent tumor. By analyses of incompatible changes i.e., genomic alterations that cannot be reversed, we show that almost all tumors from a single patient may show such changes, thus the tumors cannot have originated from each other. As recurring tumors share both genomic alterations and driver gene mutations these must have been present in the urothelium in periods with no overt tumor growth. The presence of similar mutational and CN profiles combined with incompatible events suggests that the primary and the recurrent tumors have a shared ancestry but are not originating from each other. This supports a model that includes a growing and evolving field of urothelial cells that occasionally, and locally, produce bursts of cellular growth leading to overt tumors.