Correlation between genomic alterations assessed by array comparative genomic hybridization, prognostically informative histologic subtype, stage, and patient survival in gastric cancer

Summary

It is difficult to evaluate the prognostic value of histologic criteria in gastric cancer because of the high variability of morphologic patterns. Recently, histologic subtypes of low, intermediate, or high malignant potential have been identified, providing the basis for a prognostically informative grading system. Because array comparative genomic hybridization systems allow systematic analysis of chromosome alterations, which may be prognostically and pathogenetically informative, we applied high-resolution genome-wide array comparative genomic hybridization to archival material from 81 gastric cancer cases followed for a median of 150 months after surgery. The DNA extracted from paraffin sections gave useful results in 49 tumors, 18 of which were of low-grade, 24 of intermediate, and 7 of high-grade histotypes. Based on the number of chromosome aberrations and the presence/absence of amplifications, 3 tumor clusters of increasing genomic lesion severity were constructed, which proved to correlate significantly with histologic grade and stage as well as with patient survival. Further investigation documented the lower number and severity of genomic alterations in tumors with microsatellite DNA instability and high CD8-rich lymphoid response; the close association of 8p23.1 amplification with cardial cancer; the frequent amplification of genes involved in cell renewal (CDC6, HER2, GRB7, IGFBP4) at 17q12-q21.1, with close histochemical correlation with HER2 membranous expression; and more sporadic amplification of chromosome regions harboring important oncogenes like MYC, KRAS, NRAS, CRKL, CCNE1, or ZNF217. We conclude that genome-wide array comparative genomic hybridization of gastric cancer contributes prognostically relevant information providing a genetic background for histologic grading.

Introduction

Recently, histologic subtypes of gastric cancer associated with a distinctive prognosis have been identified as a result of extensive reinvestigation of histopathologic patterns, clinicopathologic correlations, and patient survival. Muconodular expansile, very well differentiated tubular, low-grade desmoplastic, and high lymphoid (mainly of CD8-positive T cells) response (HLR) cancer subtypes were among those associated with more favorable survival, whereas diffuse anaplastic, poorly differentiated (neuro)endocrine or massively invasive mucinous cancer and a variety of rare neoplasms such as hepatoid, choriocarcinomatous, or adenosquamous carcinoma were associated with worse outcome, compared with ordinary cohesive (so called “intestinal”) or diffuse cancers [1], [2], [3], [4], [5]. Based on these prognostically informative subtypes, a comprehensive 3-grade classification of all gastric cancers was developed, which proved to be highly predictive of patient survival [6]. In addition, molecular analysis of the same series showed a correlation between high microsatellite DNA instability (MSI-H) and improved survival, when coexisting with HLR. On the other hand, a poor prognosis had been predicted by other genomic lesions, as, for instance, specific p53 mutations [6]. However, scarce information is available on genome-wide molecular analysis of prognostically informative histologic subtypes, because most of the studies published so far are based on broad tumor categories like intestinal and diffuse histotypes [7], [8], [9], [10], [11], [12] or histologically more descriptive types [13], [14], which are themselves of limited prognostic value [15], [16], rather than on histologic types specifically designed to predict patient outcome [1], [2], [3], [4], [5], [6].

In this study, a sample of 81 invasive (from T1b, deep submucosa, to T4 and stages I to IV) gastric cancers, representing the main histologic types and subtypes, were selected from a larger series of cases that had already undergone histologic, histochemical, and molecular investigation (4-6). High-resolution genome-wide array comparative genomic hybridization (aCGH) procedures were applied to DNA extracted from tumor tissue sections and the number and severity of DNA copy number aberrations (CNAs) were compared with histotypes, their proposed malignancy grades, and actual patient survival.