Microsatellite instability in young patients with colorectal cancer

Higher frequency of diploidy in young-onset microsatellite-stable colorectal cancer

PURPOSE

Colorectal carcinoma (CRC) can be divided into two nonoverlapping groups: those that are chromosomally unstable but microsatellite stable (MSS CIN+) and those that are chromosomally stable but microsatellite unstable (MSI CIN-). However, a third group with neither chromosome nor microsatellite instability (MSS CIN-) makes a substantial contribution to the total CRC burden. The clinicopathologic features of MSS CIN- CRC are not well delineated. We assessed the relationship between age and chromosomal instability (CIN) status as measured by ploidy and allelic imbalance in a series of MSS tumors.

EXPERIMENTAL DESIGN

We studied a prospectively collected series of CRC patients at Mayo Clinic Rochester. A total of 84 samples of MSS CRC in patients <or=50 years old were identified between 1994 and 1997. A consecutive series of 90 MSS CRC in patients >or=65 years old served as a comparison group. CIN status was assessed using two techniques: ploidy analysis by flow cytometry and small chromosome changes as measured by genomewide fractional allelic imbalance.

RESULTS

CRC in the young-onset group was more likely to involve the rectum and to be high stage. MSS tumors in the young-onset group were more often diploid (46%) than those in older patients (26%; P = 0.006). This difference was maintained in the subset of MSS CRC that were high stage (42% versus 18%; P = 0.02) and in rectal cancers (50% versus 23%; P = 0.04).

CONCLUSION

A greater proportion of young patients with MSS CRC has diploid tumors than patients who develop MSS CRC over age 65.

Clinicopathologic and immunohistochemistry characterization of synchronous multiple primary gastric adenocarcinoma

The aim of this investigation was to evaluate clinicopathologic and immunohistochemical characteristics of synchronous primary gastric adenocarcinomas. Immunohistochemistry for p53 (suppressor pathway) and for hMLH1, hMSH2, and hMSH6 (mutator pathway) was performed using ABC-technique amplification by biotinylated tyramide. Synchronous primary gastric adenocarcinomas were detected in 19/553 (3.43%) of the patients. The tumors were localized in distal stomach in 22, body in 14, and proximal in five. There was a predominance of intestinal type in the group of synchronic tumors compared to the solitary lesions, 73.2 vs 37.3%, p = 0.001. Synchronous neoplasias were diagnosed in earlier stage than solitary neoplasias, T1-T2 = 60.9% vs T1-T2 = 28.4%, p = 0.0001; and N0 = 68.4% vs N0 = 26.2%, p = 0.001. p53 was detected in 52.6% of the patients with synchronous tumors. Altered hMLH1 immunoexpression occurred in 26.3% of the patients and hMSH6 in 5.3%. hMSH2 immunoreactivity was positive in all tumors. p53 was solely detected in 17 tumors, while hMLH1 was altered in 10/24 negative p53 tumors, p = 0.01. Synchronous gastric adenocarcinomas presented higher frequency of intestinal type and early gastric cancer in comparison to solitary gastric cancer. Two routes of carcinogenesis, mutator, and suppressor appear to be involved independently in the development of synchronous tumors.

Genetic alterations in normal epithelium of colorectal cancer patients may be a useful indicator for subsequent metachronous tumor development

BACKGROUND

We attempted to identify areas of microsatellite alterations specific to histologically normal colorectal epithelium and to clarify the correlations among those molecular events and clinicopathologic features.

METHODS

We conducted a prospective observation study on 51 colorectal cancer patients. Preoperative blood and microdissected histologically normal colorectal epithelium and neoplastic tissues were collected. Microsatellite analyses with seven microsatellite loci were performed to examine the genetic potential of individual tumors and histologically normal colorectal epithelium.

RESULTS

In the sporadic colorectal cancer group, p53 LOH in the neoplastic epithelium had a significant correlation with the maximum tumor diameter and the preoperative serum cancer antigen 19-9 level, but not with the depth of invasion of the primary tumor. Among the patients who had p53 LOH in the histologically normal colorectal epithelium, four additional tumors were discovered within 30 months after curative surgery. For those patients, microsatellite alterations in normal colorectal epithelium were more sensitive than tumor markers.

CONCLUSIONS

For accurate LOH analysis, nonmalignant lymphocytes from blood should be used as the appropriate normal DNA sample. Focusing on the identification of high-risk patients for microsatellite alterations in histologically normal colorectal epithelium can be a useful indicator of subsequent metachronous tumor development after colorectal surgery. For accurate LOH analysis, nonmalignant lymphocytes from blood should be used as the appropriate normal DNA sample. Focusing on the identification of high-risk patients for microsatellite alterations in histologically normal colorectal epithelium can be a useful indicator of subsequent metachronous tumor development after colorectal surgery.

Distinct clinical features and outcomes of gastric cancers with microsatellite instability

Microsatellite instability (MSI) is a hallmark of the DNA mismatch repair deficiency that is one of the pathways of gastric carcinogenesis. Clinicopathologic characteristics of MSI+ gastric cancers remain unclear. To determine the correlation between MSI status and clinical features, we analyzed 327 consecutive gastric cancers for the occurrence of MSI in the BAT-26 marker. Because it has been proven that MSI at BAT-26 reflects the MSI+ phenotype, cancers with alteration at BAT-26 were categorized as having the MSI+ phenotype. The expressions of hMLH1, hMSH2, p53, MUC1, MUC2, and CEA were evaluated immunohistochemically using the tissue array method. The MSI+ phenotype was found in 9.5% (31/327) of gastric cancers examined. MSI+ gastric cancers were significantly associated with older age, antral location, Borrmann's gross Type II, intestinal subtype, lower prevalence of lymph node metastasis, and lower pTNM stage (P <.05). By multivariate logistic regression, MSI+ gastric cancers had a lower prevalence of lymph node metastasis independent of tumor invasion (P <.001). MSI+ gastric cancers displayed frequent frameshift mutations of transforming growth factor-beta type II receptor (90.3%), BAX (61.3%), hMSH3 (38.7%), and E2F4 (61.3%) genes and diminished hMLH1 (24/31) or hMSH2 (4/31) expressions. The MSI+ phenotype correlated with patient survival in advanced gastric carcinoma (P =.046). In conclusion, MSI+ phenotype in gastric cancers was found to have distinct clinicopathologic characteristics and to be predictive of a favorable outcome in advanced carcinoma.

Genetic analysis of DNA microsatellite loci in salivary gland tumours: comparison with immunohistochemical detection of hMSH2 and p53 proteins

To investigate genetic alterations in salivary gland tumours, microsatellite instability at eight representative loci and loss of heterozygosity (LOH) on chromosome 17 were analysed by polymerase chain reaction amplification. The results were compared with immunohistochemical expression of the hMSH2 and p53 proteins. Microsatellite instability and expression loss of hMSH2 protein were not recognized in the salivary gland tumours, suggesting a low frequency of abnormalities of the mismatch repair system. LOH associated with the p53 gene was detected in approximately one-half of pleomorphic adenomas and salivary carcinomas, which often showed strong p53 immunoreactivity. These features suggest that the p53 gene plays an important role in malignant transformation of salivary gland tumours. The genetic characteristics of pleomorphic adenomas might reflect a low-grade potential for malignant progression.

Features of colorectal cancers with high-level microsatellite instability occurring in familial and sporadic settings: parallel pathways of tumorigenesis

High-level microsatellite instability (MSI-H) is demonstrated in 10 to 15% of sporadic colorectal cancers and in most cancers presenting in the inherited condition hereditary nonpolyposis colorectal cancer (HNPCC). Distinction between these categories of MSI-H cancer is of clinical importance and the aim of this study was to assess clinical, pathological, and molecular features that might be discriminatory. One hundred and twelve MSI-H colorectal cancers from families fulfilling the Bethesda criteria were compared with 57 sporadic MSI-H colorectal cancers. HNPCC cancers presented at a lower age (P < 0.001) with no sporadic MSI-H cancer being diagnosed before the age of 57 years. MSI was less extensive in HNPCC cancers with 72% microsatellite markers showing band shifts compared with 87% in sporadic tumors (P < 0.001). Absent immunostaining for hMSH2 was only found in HNPCC tumors. Methylation of hMLH1 was observed in 87% of sporadic cancers but also in 55% of HNPCC tumors that showed loss of expression of hMLH1 (P = 0.02). HNPCC cancers were more frequently characterized by aberrant beta-catenin immunostaining as evidenced by nuclear positivity (P < 0.001). Aberrant p53 immunostaining was infrequent in both groups. There were no differences with respect to 5q loss of heterozygosity or codon 12 K-ras mutation, which were infrequent in both groups. Sporadic MSI-H cancers were more frequently heterogeneous (P < 0.001), poorly differentiated (P = 0.02), mucinous (P = 0.02), and proximally located (P = 0.04) than HNPCC tumors. In sporadic MSI-H cancers, contiguous adenomas were likely to be serrated whereas traditional adenomas were dominant in HNPCC. Lymphocytic infiltration was more pronounced in HNPCC but the results did not reach statistical significance. Overall, HNPCC cancers were more like common colorectal cancer in terms of morphology and expression of beta-catenin whereas sporadic MSI-H cancers displayed features consistent with a different morphogenesis. No individual feature was discriminatory for all HNPCC cancers. However, a model based on four features was able to classify 94.5% of tumors as sporadic or HNPCC. The finding of multiple differences between sporadic and familial MSI-H colorectal cancer with respect to both genotype and phenotype is consistent with tumorigenesis through parallel evolutionary pathways and emphasizes the importance of studying the two groups separately.

MLH1 and MSH2 protein immunohistochemistry is useful for detection of hereditary non-polyposis colorectal cancer in young patients

AIMS

Hereditary non-polyposis colorectal cancer is related to germline mutations of DNA mismatch repair genes MLH1 and MSH2, which result in microsatellite instability and loss of protein expression of the corresponding mutated gene in the tumour tissue.

METHODS AND RESULTS

MLH1 and MSH2 protein expression was studied by immunohistochemistry in paraffin-embedded surgical samples of 100 colorectal adenocarcinomas occurring before 50 years of age. Absence of tumour cell nuclear staining with positive internal control (normal mucosa, lymphoid follicles) was considered negative. Loss of MLH1 or MSH2 expression was found in 20 cases with microsatellite instability in 15 cases. Twelve of these patients had a family history of colorectal cancer. Compared with MLH1- and MSH2-positive cases, MLH1- or MSH2-deficient colorectal adenocarcinomas were significantly associated on multivariate analysis with a younger age (38 vs. 43 years, P;0.0224), a larger tumour size (60 +/- 6 vs. 46 +/- 2 mm, P=0.0291), an expanding margin (85% vs. 51%, P=0.0159), a higher number of tumour-infiltrating lymphocytes assessed by CD3 immunostaining (202 +/- 48 vs. 33 +/- 4 CD3+ lymphocytes/10 high-power fields, P=0.0039), and a grade 2 Crohn's like lymphoid reaction (70% vs. 9%, P=0.0037). The two groups were not different for tumour site, differentiation, pTNM stage, vascular and perineural invasion, peripheral adenomatous residue, and 5-year survival rates.

CONCLUSIONS

MLH1- or MSH2-deficient colorectal carcinomas of young patients exhibit pathological and molecular features similar to hereditary non-polyposis colorectal cancer. This suggests that MLH1 and MSH2 immunohistochemistry is valuable for detecting hereditary non-polyposis colorectal cancer in young patients.

Microsatellite instability is a predictive marker for survival benefit from adjuvant chemotherapy in a population-based series of stage III colorectal carcinoma

Tumors with the microsatellite instability (MSI) phenotype appear to comprise a biologically and clinically distinct group of colorectal carcinomas (CRC). MSI+ has been associated with favorable prognosis; however, it is not clear whether this is because MSI+ tumors are inherently less aggressive or because they are more sensitive to chemotherapy. We investigated the prognostic and predictive significance of this molecular alteration along with its association with nodal burden in a large, population-based cohort of stage III CRC patients. Eight hundred seventy-six stage III CRC patients with long median follow-up (76 months) were included in the study. MSI status was determined by screening for deletions in the BAT-26 mononucleotide repeat. Systemic adjuvant fluoropyrimidine-based chemotherapy was delivered to 266 patients (30%). MSI+ was more common in tumors from female patients and tumors that originated in the proximal colon. It was predictive of excellent survival benefit from chemotherapy but was not associated with better prognosis for patients who did not receive treatment. Lower nodal burden was a prognostic factor for improved survival. MSI+ was associated with lower nodal burden in the overall group (P = 0.02, chi 2 test) but not for patients who received chemotherapy. In stage III CRC, MSI+ was not prognostic in nonadjuvant-treated patients, suggesting that the biological behavior of MSI+ tumors in the absence of chemotherapy is the same as MSI- tumors. Tumors with the MSI+ phenotype appear to be more sensitive to chemotherapy, as observed by improved survival for patients receiving this treatment. MSI along with other molecular markers could be used in the future for a more refined selection of CRC patients to receive fluoropyrimidine-based chemotherapy.

Prognostic relevance of hMLH1, hMSH2, and BAX protein expression in endometrial carcinoma

Endometrial carcinoma is the most common gynecologic malignancy in perimenopausal and postmenopausal women. A role of mismatch repair genes, like hMLH1 and hMSH2 in their pathogenesis, has been suggested. Loss of their function leads to the accumulation of replication errors (mutator phenotype), which are responsible for further mutations in genes with microsatellite sequences in their coding region, such as Bax. We analyzed the expression of hMLH1, hMSH2, and Bax genes in 89 formalin-fixed paraffin-embedded endometrial carcinomas. The immunostains were scored with regard to percentage of positive tumor cells (0%, <10%, 10 to 50%, >50%), and relative staining intensity (1+, 2+, 3+). The staining results were correlated with clinicopathologic features and survival. Loss of hMSH2 expression (0% positive cells) was observed in 1.1% (1/89) of the tumors; loss of hMLH1 was seen in 12.4% (11/89) of the cases, particularly in endometrioid tumors with mucinous differentation (5/11; 45%; P =.03). No significant association was found between the immunoscores and grade, stage criteria of the International Federation of Obstetrics and Gynecology (FIGO), or age of the patients. Among 11 tumors with loss of Bax expression (12.4%), 4 had also loss of hMLH1 (4/11; 36.4%; P =.017). In multivariate analysis (Cox model), significantly longer survival was found for patients with tumors in FIGO Stage I-II (P <.0001), endometrioid type (P =.001), low grade (P =.001), and absence of hMLH1 expression (P =.027). Our results suggest that loss of function of hMLH1 and Bax occur in a subgroup of endometrial carcinoma. In addition to the classical prognostic factors, absence of hMLH1 expression is associated with better outcome of patients.

High frequency of microsatellite instability in young patients with head-and-neck squamous-cell carcinoma: lack of involvement of the mismatch repair genes hMLH1 AND hMSH2

The most prevalent risk factors in the development of head-and-neck squamous-cell carcinoma (HNSCC) are excessive tobacco and alcohol consumption. In young patients with HNSCC, these risk factors are often absent. Our purpose was to investigate the risk factors, microsatellite instability (MSI) changes and status of the mismatch repair genes hMLH1 and hMSH2 in a cohort of young patients with HNSCC. Fifty-seven HNSCC tumors were examined for the presence of MSI at 16 microsatellite sites using PCR. In the young patient group (24 cases, < or = 44 years old), 100% of tumors had MSI at 1 site at least and 88% had MSI at 2 or more loci. In older patients (33 cases, > or = 45 years), MSI at 1 or more sites was found in 61% of tumors (young vs. old, p = 0.0003) and instability at 2 or more sites was found in 36% of tumors (young vs. old, p = 0.0001). The involvement of the mismatch repair genes was investigated by examining promoter methylation, exon mutation and gene expression of hMLH1 and hMSH2. All results were negative, indicating that inactivation of these 2 genes does not play a role in the development of MSI in tumors from this patient group. Furthermore, the young patient group had a significantly lower incidence of smoking (46% young, 88% old; p = 0.001) and alcohol consumption (33% young, 67% old; p = 0.0169), emphasizing the probable importance of other environmental and/or genetic factors in the development of their disease.

Microsatellite instability in synchronous gastric carcinomas

Synchronous gastric carcinomas are found in 4% to 10% of all gastric carcinomas, and the tumor multiplicity is believed to be related to genetic predisposition. To investigate the role of mismatch repair error in synchronous gastric carcinomas, we analyzed the microsatellite instability (MSI) status of 101 cancers from 48 gastrectomy specimens and compared them with 149 solitary gastric carcinomas. Multiple synchronous gastric carcinomas are characterized by slightly older age, predominance in males, early stage and lower lymph node metastasis. Among the 48 cases, 8 (18 lesions) were associated with a gastric adenoma (type I) and 40 (83 lesions) were not associated with a gastric adenoma (type II). The MSI+ rate was 50% in the type I and 8.4% in the type II synchronous gastric carcinomas (p < 0.001), while that of solitary gastric carcinomas was 9.4%. In addition, the frameshift mutation rates of the TGF-betaRII, BAX and hMSH3 genes in the type I synchronous carcinomas were higher than those in the type II synchronous carcinomas. These findings indicate that a defect in the mismatch repair system might play a role in the carcinogenesis of a minor subset of multiple gastric carcinomas associated with adenomas.

Heterogeneity of p53 mutational status in intramucosal carcinoma of the colorectum

The aim of this study was to elucidate whether or not p53 genetic heterogeneity would occur while colorectal carcinoma was limited to the mucosa. Eight cases of endoscopically resected colorectal intramucosal carcinomas were analyzed to determine the p53 gene sequence (exons 5 to 8). Six out of 8 cases showed p53 gene mutations, and in all of them, the mutational status was heterogeneous. In 4 cases, mutated codons were heterogeneous as well. These data indicate that p53 gene alterations in colorectal carcinomas occur and diverge at the stage of intramucosal carcinoma, supporting our previously proposed hypothesis that colorectal carcinomas can be composed of various subclones as regards p53 gene mutation, while the carcinoma is limited to the mucosa, and one of these subclones commences invasion to the submucosa after clonal selection, thus generating a monoclonal invasive carcinoma.

[Colorectal cancer in patients younger than 40 years of age]

Between 1988 and 1994, 326 patients with colorectal cancers were treated at the Ibn Rochd Oncology Centre in Casablanca; 88 patients were less than 40 years old (27%). There were 79 males and nine females. A family history of colorectal cancer was noted in 5%. The most frequent symptoms were bleeding and rectal pain. The localisation of the tumour was the rectum in 70 cases. According to the anatomopathological profile, Dukes stages C and D were the most frequent and mucosal adenocarcinoma was noted in 24 cases. Seventy patients had surgery, associated with radiation therapy in 59 cases. Adjuvant chemotherapy was given in 44 cases and palliative treatment in 17 cases. Recurrence occurred in 14 cases and metastasis in other six cases. At five years, overall survival and disease-free survival rates were 24% and 17%, respectively. Worse prognostic factors were mucosal adenocarcinoma, poor differentiated adenocarcinoma and Dukes C and D stages.

Genetic alterations in gastric cancer cell lines and their original tissues

To investigate the genetic changes that occur during establishment of gastric cancer cell lines, 4 gastric cancer cell lines and their original tumor tissues were examined for microsatellite instability (MSI), loss of heterozygosity (LOH), and p53 mutation. MSI status did not change during the establishment, though the cell lines gained frameshift mutation in some of the genes with polytract coding sequences. There was no difference in p53 mutation between the cell lines and the original tumors. The frequency of LOH was similar between the cell lines and each original tumor, in the range 30.8% to 85.7%. The difference in the LOH results between the cell lines and the original tumors was not greater than the difference between the different areas of the original tumors. The above results suggested that most of the genetic alterations, such as MSI, LOH, and p53 gene mutation, were sustained during the establishment of gastric cancer cell lines. Minor genetic differences between original tumor tissues and cancer cell lines could be explained as a tumor heterogeneity because separate areas of the original tumor tissues manifest similar variations.

Broadsheet number 52: Molecular genetics of colorectal cancer

The molecular genetics of colorectal cancer is presented in an order that ascends from the basic to the applied: molecular mechanisms, morphogenesis, classification and diagnosis. Major consideration is given to the nature of genetic instability and the role of this mechanism in driving neoplastic progression. It is shown how the fundamental principle of genetic instability cuts across applied research, tissue diagnosis and clinical management with respect to both sporadic and inherited forms of colorectal cancer.