Genetic Susceptibility to Distinct Bladder Cancer Subphenotypes

Abstract

Background

Clinical, pathologic, and molecular evidence indicate that bladder cancer is heterogeneous with pathologic/molecular features that define distinct subphenotypes with different prognoses. It is conceivable that specific patterns of genetic susceptibility are associated with particular subphenotypes.

Objective

To examine evidence for the contribution of germline genetic variation to bladder cancer heterogeneity.

Design, setting, and participants

The Spanish Bladder Cancer/EPICURO Study is a case-control study based in 18 hospitals located in five areas in Spain. Cases were patients with a newly diagnosed, histologically confirmed, urothelial cell carcinoma of the bladder from 1998 to 2001. Case diagnoses were reviewed and uniformly classified by pathologists following the World Health Organisation/International Society of Urological Pathology 1999 criteria. Controls were hospital-matched patients (n = 1149).

Measurements

A total of 1526 candidate variants in 423 candidate genes were analysed. Three distinct subphenotypes were defined according to stage and grade: low-grade nonmuscle invasive (n = 586), high-grade nonmuscle invasive (n = 219), and muscle invasive (n = 246). The association between each variant and subphenotype was assessed by polytomous risk models adjusting for potential confounders. Heterogeneity in genetic susceptibility among subphenotypes was also tested.

Results and limitations

Two established bladder cancer susceptibility genotypes, NAT2 slow-acetylation and GSTM1-null, exhibited similar associations among the subphenotypes, as did VEGF-rs25648, which was previously identified in our study. Other variants conferred risks for specific tumour subphenotypes such as PMS2-rs6463524 and CD4-rs3213427 (respective heterogeneity p values of 0.006 and 0.004), which were associated with muscle-invasive tumours (per-allele odds ratios [95% confidence interval] of 0.56 [0.41–0.77] and 0.71 [0.57–0.88], respectively) but not with non–muscle-invasive tumours. Heterogeneity p values were not robust in multiple testing according to their false-discovery rate.

Conclusions

These exploratory analyses suggest that genetic susceptibility loci might be related to the molecular/pathologic diversity of bladder cancer. Validation through large-scale replication studies and the study of additional genes and single nucleotide polymorphisms are required.

Introduction

Urothelial cell carcinoma of the bladder (UCCB) is the fifth most common cancer in men; it occurs with a male-to-female ratio of approximately 3:1. Spain has one of the highest incidence rates among men (55 per 100 000) yet one of the lowest among women (7.4 per 100 000), with a male-to-female ratio of 7:1 [1]. Because of its commonly indolent course, UCCB is one of the most expensive cancers in terms of medical care costs per patient [2].

Pathologic and molecular evidence suggest that UCCB is not a unique phenotype. Based on stage, tumours are classified as non–muscle invasive and muscle invasive, the former representing approximately 80% of cases at presentation. Non–muscle-invasive tumours are subclassified into low and high grade. Tumours of these subphenotypes have different biologic behaviour and are associated with distinct patient prognosis [3], [4], [5]. This classification has been supported by the identification of molecular alterations that identify two major genetic pathways leading to low-grade, genomic stable and high-grade, genomic unstable tumours, the latter including a proportion of non–muscle-invasive tumours and the vast majority of muscle-invasive tumours. Activating mutations in FGFR3 and PI3KCA are associated with low-grade non–muscle-invasive tumours, whereas p53 and retinoblastoma (RB) pathway alterations are critical for high-grade nonmuscle-invasive and muscle-invasive tumours (Fig. 1) [6], [7]. However, the precise mechanisms through which tumours evolve need to be more precisely defined.

The aetiology of UCCB is multifactorial, with both environmental and genetic factors identified. The best established exogenous risk factors are tobacco and occupational exposure to aniline dyes and aromatic amines [8], [9]. Their influence on UCCB risk is similar for tumours of varying stages and grades [10]; thus exogenous risk factors cannot currently explain disease heterogeneity. UCCB is also one of the tumours for which a role of low-penetrance genetic variants, such as GSTM1-null and NAT2-slow, has been best established [11]. Furthermore, strong evidence indicates an interaction between the NAT2-slow variant and smoking [11]. Other genetic polymorphisms have been reported to be associated with UCCB risk, but replication is necessary to establish risk conclusively [12], [13]. One explanation for this lack of success is that polymorphisms may exhibit a small to moderate effect only within particular subphenotypes of the disease [6], [14]. Thus polymorphisms that may be important for a particular subphenotype could be overlooked in an analysis that pools the subphenotypes due to an attenuation of effects.

The aim of this work is to investigate whether UCCB subphenotypes defined according to clinicopathologic characteristics have different associations with germline polymorphisms in the Spanish Bladder Cancer (SBC)/EPICURO (EPIdemiology of Cancer of the UROthelium) Study. Although this approach has been recently applied to breast [14] and prostate cancer [15], this report is the first to do so for UCCB. A total of 1526 polymorphisms in 423 cancer candidate genes were examined with respect to three distinct UCCB subphenotype groups.