Original Article
Clinicopathologic characteristics of colorectal cancer with microsatellite instability

https://doi.org/10.1016/j.prp.2013.10.004Get rights and content

Abstract

Colorectal cancer (CRC) can be classified according to the level of microsatellite instability (MSI) exhibited by the tumor. The aim of this study was to determine MSI status in CRC from Tunisia and to identify clinical and pathological characteristics of MSI-H tumors.

Microsatellite status was determined by polymerase chain reaction amplification using standard markers (BAT25, BAT26, D2S123, D5S346 and D17S250, the Bethesda panel) in 44 CRC cases. Molecular results were correlated with pathological and clinical features.

Six CRC cases (13.8%) showed high-level instability (MSI-H), 14 cases had low level instability (MSI-L), and the remainders were stable (MSS). Immunohistochemical analysis showed loss of MSH2 protein in 3 cases among the 6 MSI-H tumors, whereas no silencing of MLH1 or MSH6 was found in any case. Significant differences in age and family history of cancers were observed between MSI-H and MSS/MSI-L groups (p = 0.01 and p = 0.002). However, statistical analysis showed that there were no significant differences between MSI-H and MSS/MSI-L tumors in terms of tumor location, lymph node involvement and stage of disease. Regarding histological features, MSI-H tumors were more likely to be poorly differentiated (p = 0.003), to have a medullary pattern (p = 0.005), and to harbor increased numbers of peritumoral lymphocytes (p = 0.001).

These findings indicate that careful observation of the tumor morphology can assist in the identification of unstable colorectal cancers requiring molecular investigations.

Introduction

Colorectal cancers (CRC) are considered to belong to the most common cancers in industrialized countries. They are the third most common cancer in men after lung and prostate cancers and come second in women after breast cancer. In Tunisia, CRC have an annual incidence of 10.3/100,000 individuals. However, a significant proportion (9%) of these cancers occurs before age 40 years, suggesting genetic susceptibility [13].

The deficiency of the DNA mismatch repair (MMR) system is a major mechanism for carcinogenesis. It is involved in the development of hereditary non-polyposis colorectal cancers (HNPCC, also called Lynch syndrome) and in nearly 20% of sporadic CRC [3]. This deficiency is responsible for microsatellite instability (MSI), resulting from the accumulation of small insertions or deletions that frequently arise during replication of these short repeated sequences [25].

Dysfunction of MMR proteins may be related either to an alteration of a gene at the constitutional level, which is the case with Lynch syndrome mutations constitutional MMR genes (hMLH1, hMSH2, hPMS1, hPMS2 and hMSH6), or to altered gene in somatic tumor. In the latter case, it is often a loss of function of hMLH1 most often involved is its epigenetic repression by methylation of its promoter [34].

Determining the MSI phenotype by molecular biology techniques has been standardized by the international conference organized by the National Institute of Health in 1998 [3], which recommends the genotyping of five markers: three dinucleotide repeat markers (D2S123, D5S346, D17S250) and two mononucleotide repeat markers (BAT25 and BAT26) [3]. The realization of this phenotype, which compares the constitutional and tumor genome of a patient, assumes control of the histological quality of the tumor sample.

Besides a fundamental interest because of the original transformation mechanism, the study of tumors with MSI instability is of great clinical interest. It has indeed been shown in several studies that tumors with MSI had several epidemiological, anatomical, histological and prognostic features [1], [14], [39].

The aim of the present study was to analyze in a series of CRC from Tunisia the clinico-pathological characteristics of colorectal cancers with microsatellite instability.

Section snippets

Patients and tumor samples

Patients who had undergone resection of CRC between January and December 2007 were identified from the files of the Department of Pathology, CHU Farhat-Hached of Sousse, Tunisia. Patients with history of familial adenomatous polyposis or preoperative anticancer therapy were excluded from the study. Fifty patients were retained for this study. For all of these cases, matched pairs of colorectal tumor and normal adjacent tissues were obtained as formalin-fixed, paraffin-embedded specimens.

MSI detection

The quality of DNA samples was checked by PCR amplification of a 268-pb fragment within the human β-globin gene. The integrity of DNA samples was validated in 44 of the 50 CRC cases tested. MSI analyses were then performed for these 44 CRC cases. Of these, 24 patients (54.5%) were found to have MSS tumors, 14 patients (31.8%) had instability at one marker (MSI-L), and six patients (13.6%) had instability at two or more markers (MSI-H). Fig. 1 illustrates representative examples for MSI analysis.

Discussion

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent cause of inherited colorectal cancer. It is an autosomal dominantly inherited syndrome characterized by the occurrence of early onset CRC, an excess of synchronous and metachronous CRC, as well as a defined spectrum of extracolonic tumors, particularly cancers of the endometrium, small intestine, hepato-biliary tract, upper urinary tract and stomach [23]. Most of these cases remain unknown for lack of a suitable diagnostic

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgements

This work was supported by the “Ministère de l’Enseignement Supérieur, de la Recherche Scientifique et Technologie” and the “Ministère de la Santé” of Tunisia.

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