Loss of heterozygosity and microsatellite instability in de novo versus ex-adenoma carcinomas of the colorectum

Role of topoisomerase I and thymidylate synthase expression in sporadic colorectal cancer: associations with clinicopathological and molecular features

Topoisomerase I (Topo I) and thymidylate synthase (TS) are essential enzymes for the replication, transcription and repair of DNA, and are potential biomarkers in colorectal cancer (CRC). The aim of the study was to correlate the tissue expression of Topo I and TS in sporadic CRCs with relevant pathological and molecular features and patients' outcome. Topo I and TS expression was assessed by immunostaining in 112 consecutive primary CRCs. Increased expression of Topo I was found in 36% of tumors, preferentially rectal (50%) and with not otherwise specified (NOS) histology (44%). Topo I expression was associated with 18q allelic loss (LOH), (p=0.013), microsatellite stable phenotype (p=0.002) and normal expression of mismatch proteins hMLH1 and hMSH2 (p=0.0012 and p=0.02, respectively). High TS expression was found in 60% of tumors, more frequently in distal sites (62%) and with NOS histology (66%); no association with microsatellite instability was observed. Topo I seems to be involved in the chromosomal instability pathway of sporadic CRCs. Conversely, high TS expression is unlikely to affect the clinical behavior of microsatellite unstable CRCs.

Sporadic colorectal carcinomas with low-level microsatellite instability: a distinct subgroup with specific clinicopathological and molecular features

PURPOSE

The biologic significance of low-level microsatellite instability (MSI) in sporadic colorectal cancers (CRCs) is not clearly defined. In particular, the relationship of MSI-low to MSI-high and microsatellite stable (MSS) tumours is currently under debate and the prognostic impact of these genetic changes remains unclear. The objective of this study was to investigate whether sporadic MSI-low CRCs have different clinicopathological and molecular features from MSS and MSI-high tumours.

METHODS

A series of 184 primary sporadic CRCs were divided, according to the level of MSI, into three groups (94 MSS, 22 MSI-low and 68 MSI-high) and were analyzed for baseline clinicopathological features and outcome, allelic losses at 18q, 8p and 4p chromosomes and immunohistochemical expression of MGMT, hMlh1, hMsh2, Fhit, Cox-2, p21 and p27 proteins.

RESULTS

MSI-low tumours were more frequently distal (59.1%) whereas MSS tumours had a strong predilection for distal (72.3%) and MSI-high tumours for proximal location (54.4%; p = 0.003). When compared with MSI-high tumors, MSI-low CRCs were adenocarcinoma, not otherwise specified (p = 0.0138) and well to/moderately differentiated (p = 0.027). MSI-low CRCs also showed specific molecular features including intermediate 18q allelic losses, altered MGMT and Cox-2 expression. Finally, the 5-year overall survival rates were 79% for MSI-low, 40.3% for MSS and 71% for MSI-high CRCs (p = 0.0160 MSS vs. MSI-low groups).

CONCLUSIONS

Sporadic MSI-low CRCs display characteristic clinicopathological and genetic features that distinguish them from MSS CRCs.

[Differential diagnostics of hereditary colorectal cancer syndromes. The role of pathology]

One third of colorectal carcinomas (CRC) show familial clustering of which about 5% have a monogenetic trait. Distinction between disease with and without polyposis, tumor histology and tumor spectrum in a given patient are all of diagnostic relevance. Familial adenomatous polyposis (FAP) underlies approximately 1% of CRC characterized by rapidly forming (>100) adenomas. In contrast to these about 2%-3% of CRC have a hereditary background without polyposis (HNPCC). This is the only hereditary tumour syndrome to date for which a tissue-based molecular screening test is available. Accordingly, expression analysis of mismatch repair genes (MSH2, MSH6 and MLH1, PMS2) is performed first. In the case of an equivocal result with no complete loss of expression testing of microsatellite instability (MSI) is added. In contrast to the other diseases MYH-associated polyposis (MAP) follows a recessive trait with polyp numbers usually between 15-30 adenomas and should be distinguished from attenuated forms of FAP with <100 polyps in the differential diagnosis. In the case of suspected familial cancer syndrome genetic counseling is warranted in order to decide ultimately whether there is an indication for genetic testing (evidence of a germ-line mutation).

Prognostic values of chromosome 18q microsatellite alterations in stage II colonic carcinoma

AIM: To investigate the prognostic value of chromosome 18q microsatellite alterations (MA) in stage II colon cancer.

METHODS: One hundred and six patients with sporadic stage II colon cancer were enrolled in this study. DNA was extracted from formalin-fixed, paraffin-embedded tumor and adjacent normal mucosal tissue samples. MA, including loss of heterozygosity (LOH) and microsatellite instability (MSI), was analyzed by polymerase chain reaction, polyacrylamide gel-electrophoresis and DNA sequencing at 5 microsatellite loci on chromosome 18q (D18S474, D18S55, D18S58, D18S61 and D18S64).

RESULTS: Among the 102 patients eligible for MA information, the overall frequencies of LOH, high and low frequency MSI/microsatellite stable were 49.0%, 17.6% and 82.4%, respectively. The high frequency of 18q-LOH was significantly associated with the poor 5-year overall survival (OS) (P = 0.008) and disease free survival (P = 0.006). High levels of MSI were significantly associated with a longer 5-year OS (P = 0.045) while the higher frequency of 18q-LOH at the loci of D18S474 and D18S61 was significantly associated with a poorer 5-year OS (P = 0.010 and 0.005, respectively). But multivariate analysis showed that only the frequency of 18q-LOH was significantly associated with the prognosis of the disease.

CONCLUSION: High frequency of 18q-LOH is an independent prognostic factor indicating poor prognosis of the patients with stage II colon cancer.

Genetic aspects of non-polypoid colorectal neoplasms

Colorectal cancer is a heterogeneous disease arising through multiple possible pathways. Elucidating the genetic factors controlling molecular phenotype, morphology, histology, and prognosis of different tumor types continues to be a challenge. Non-polypoid colorectal neoplasms provide opportunities for ongoing study of their underlying genetic abnormalities and molecular phenotypes. The varied data from different groups, however, highlight the need for further studies in different populations.

Two subtypes of mucinous adenocarcinoma of the colorectum: clinicopathological and genetic features

BACKGROUND

This work is aimed at comparing mucinous colorectal adenocarcinomas (MUC) and non-mucinous colorectal adenocarcinomas (non-MUC), and at verifying the existence of two different subgroups of MUC, in terms of clinicopathological features, chromosomal alterations, and outcome, in a geographical area where mucinous colorectal cancer resulted as being very frequent.

METHODS

One hundred and fifty-six unselected patients who underwent curative colorectal resection for sporadic colorectal cancer over a 4-year period were evaluated for histological classification as to MUC and non-MUC subtype, for microsatellite instability (MSI) using six microsatellite markers, and for the presence of p27, Fhit, and cyclooxygenase-2 (Cox-2). Molecular data, immunohistochemical results, recurrence frequency, and patient survival were analyzed statistically in relation to histological subtypes.

RESULTS

MUC accounted for 38.5% of all colorectal carcinomas. Compared to non-MUCs, MUCs were more frequently located in the proximal colon (p < 0.001), and more frequently showed MSI phenotype (p < 0.001), altered protein expression of hMlh1 (p = 0.030), Fhit (p <0.001), and p27 (p < 0.001). Compared to MUC with microsatellite-stable (MSS) phenotype, MUC with MSI more frequently resulted as being located in the proximal colon (p = 0.013), and more frequently showed altered expression of hMlh1 (p < 0.001), hMsh2 (p = 0.008), Fhit (p < 0.001), and p27 (p = 0.015). Significantly better survival of patients with proximal MUC (p = 0,012), with MSI MUC (p = 0.017), and with MUC with altered p27 expression (p = 0.02).

CONCLUSION

The results of the present study confirm that MUC represents distinct clinicopathological and genetic features as compared to non-mucinous tumors and support the hypothesis that MUC includes two subtypes with different genetic pathways and behavior.

Loss of p27 expression and microsatellite instability in sporadic colorectal cancer

BACKGROUND

The role of the loss of p27 protein expression in the oncogenesis of colorectal cancer is still in debate. In this study, we prospectively examined the immunohistochemical expression of p27 in 108 consecutive colorectal cancers, and we analysed the relationship with the results, the clinicopathological data, microsatellite instability (MSI) and other genetic alterations of tumours.

METHODS

Unselected patients (108) who underwent curative colorectal resection for sporadic colorectal cancer in a three-year period were evaluated for MSI using 6 microsatellite markers, and for the presence of p27, p53, Fhit, Mlh1 and Msh2 proteins by means of immunostaining. The relationships between these markers were analysed. p27 protein expression was examined for association with disease recurrences and survival.

RESULTS

Lack of p27 expression was noted in 33 out of 108 (30.5%) colorectal cancer cases (P<0.05). This altered expression was significantly higher in proximal cancers (P<0.05), mucinous tumours (P<0.001), poorly differentiated histology (P<0.01), cancers with MSI (P<0.05), tumours with altered expression of Mlh1 (P<0.01), of Msh2 (P<0.05), and of Fhit (P<0.01). Overall survival was better in the patient group with altered level of phenotypic p27 expression, although the difference does not reach statistical significance (P=0.069). The analysis performed only for patients with tumour at stage II showed significantly better survival when the tumour exhibited altered p27 expression (P<0.02).

CONCLUSIONS

The results of the present study support the hypothesis that altered expression of p27 may be part of the genetic pathway involving MSI, which is responsible for the development of some colorectal cancers.

Clinicopathologic and immunohistochemical study of small apparently "de novo" colorectal adenocarcinomas

Rarely, adenocarcinomas of the colorectum develop as small (< or =1.0 cm) rapidly invasive tumors without an obvious adenomatous or "in situ" component. These tumors have been termed "de novo" carcinomas. Although it is believed by some that these tumors are more aggressive than conventional large adenocarcinomas with an identifiable in situ component, little is known about the biologic characteristics and natural history of these lesions. The aim of this study was to evaluate and compare the pathologic features, biologic characteristics, and natural history of small apparently de novo invasive colorectal adenocarcinomas with conventional large (>1.0 cm) carcinomas. Routinely processed specimens from 20 patients (M/F ratio: 13/7; mean age: 65 y) with small apparently de novo invasive colorectal adenocarcinomas (all < or =1.0 cm in size) were evaluated for a variety of clinical and pathologic features. In addition, immunostains for p53, beta-catenin, DPC4, hMLH1, hMSH2, and MGMT were evaluated in all cases. The findings in this group of cases were compared with those from 20 control patients (M/F ratio: 8/12; mean age: 60 y) with stage-matched conventional "large" colorectal adenocarcinomas (all >1.0 cm in size). Patients were followed for a mean of 52.6 and 60.6 months, respectively, for the 2 groups. Small apparently de novo invasive adenocarcinomas were present in the left colon, transverse colon, and right colon in 85%, 10%, and 5% of cases, respectively. Their mean size was 7 mm (range: 3 to 10 mm). All cases were stage T1 and the majority were moderately differentiated (75%). Only 1 (5%) patient had lymph node metastases. Two (10%) cases were mucinous and only 1 (5%) showed prominent tumor infiltrating lymphocytes. Upon complete sectioning of the tissue blocks of tumor, residual foci of adenomatous epithelium were present in 16/20 (80%) cases, of which 75% contained foci of high-grade dysplasia. P53 and nuclear beta-catenin staining was present in 70% and 85% of cases, respectively, but only 5 cases (25%) showed loss of DPC4. Loss of MGMT expression was seen in 5 cases (25%), loss of hMSH2 in only 1 case (5%), and none showed loss of hMLH1. Only 2 patients (10%) developed visceral metastases upon follow-up. Control patients had similar demographic features, clinical outcome, anatomic distribution of tumors, degree of differentiation, and prevalence of positivity for the immunostains noted above, to the study cases. In our patient population, true small de novo colorectal adenocarcinomas, tumors that lack an identifiable adenomatous component, are exceedingly rare, because complete tissue sectioning reveals residual adenomatous tissue in the majority of cases. The biologic characteristics and natural history of small carcinomas with a minimal dysplastic component, and those with no identifiable adenomatous component, are similar to conventional large (>1 cm) adenocarcinomas, and, thus, they should probably be treated similarly.

Distinct molecular patterns based on proximal and distal sporadic colorectal cancer: arguments for different mechanisms in the tumorigenesis

BACKGROUND AND AIMS

Colorectal cancer (CRC) ranks as the fourth most frequently diagnosed cancer worldwide. CRCs that arise proximally or distally to the splenic flexure show differences in epidemiologic incidence, morphology, and molecular alterations, suggesting the existence of two categories of CRC based on the site of origin. The aim of the present work is to investigate the histological and molecular differences between CRCs located proximally and distally to the splenic flexure, and their potential involvement in tumor prognosis and therapeutic strategies.

METHODS

We evaluated 120 patients affected by sporadic CRC for clinicopathologic features, microsatellite instability (MSI), loss of heterozygosity (LOH) of chromosomes 18q, 8p, and 4p; they were also investigated for hMlh1, hMsh2, Fhit, p27, and Cox-2 immunostaining.

RESULTS

The mucinous histotype was more frequent in the proximal than in the distal CRCs (p<0.004). The frequency of MSI phenotype was higher in proximal than in distal tumors (p<0.001); moreover, reduced or absent hMlh1, Fhit, p27 immunohistochemical expressions were more frequent in proximal than in distal tumors (p<0.001 and 0.01 for p27). In contrast, the frequency of LOH in 18q was higher in distal than in proximal tumors (p=0.002). No significant differences were observed between proximal and distal tumors in the frequency of LOH in 8p and altered expression of hMsh2 and p53 protein.

CONCLUSION

These different features may reflect different genetic pathways of carcinogenesis and support the hypothesis of a different mechanism of cancer development between the proximal and the distal colon, with potential implications in the therapeutic approach.

Genetic instability on chromosome 17 in the epithelium of non-polypoid colorectal carcinomas compared to polypoid lesions

Early colorectal carcinomas (submucosal invasive adenocarcinomas) can be classified into polypoid growth carcinoma (PG-Ca) and non-polypoid growth carcinoma (NPG-Ca) types, the latter transforming more rapidly to advanced carcinoma. Previously, we indicated that stromal genetic instability might contribute to tumorigenesis of both sporadic and ulcerative colitis-associated colorectal adenocarcinomas. In the present study, we analyzed genetic instability of both epithelial and surrounding stromal components in PG-Ca and NPG-Ca. In 99 colorectal submucosal invasive adenocarcinomas, epithelial and stromal genetic instability was analyzed with National Cancer Institute standard microsatellite markers, chromosome 17 (Chr.17) markers and tumor suppressor gene-related markers, using a combination of the laser-captured microdissection and GeneScan approaches. Immunohistochemical analysis was carried out for hMLH1, hMSH2, MGMT and p53. In addition, we investigated methylation of the hMLH1 and MGMT promoters. The frequencies of epithelial microsatellite instability (MSI) with Chr.17 markers were significantly higher in NPG-Ca (33.3%) compared to PG-Ca (10.4%), particularly with D17S579 and D17S796. For loss of heterozygosity, only D17S786 showed a significant difference. The frequencies of stromal MSI with all markers were 31.7% and 25.9% in NPG-Ca and PG-Ca, respectively, but D17S579 and TP53 showed higher MSI in NPG-Ca than PG-Ca. Immunohistochemically, p53 protein expression in PG-Ca was significantly higher in loss of heterozygosity-positive cases with altered Chr.17 markers overall, especially the D17S796 marker, compared to cases without genetic instability. These results suggest that epithelial and stromal MSI of Chr.17 markers contributes more to carcinogenesis in NPG-Ca, whereas stromal genetic instability might be necessary for the development of both types of colorectal carcinoma.

Mutational analysis of beta-catenin and the RAS-RAF signalling pathway in early flat-type colorectal tumours

Morphologically, early colorectal tumours can be divided into two groups, protruded-type and flat-type. However, little is known about genetic mechanisms of the latter. We investigated mutations of beta-catenin, KRAS, BRAF, and PIK3CA in 310 early colorectal tumours. beta-catenin mutation was detected in 7.1% of 310 tumours. beta-catenin mutation was detected in a significantly higher percentage of flat-type tumours with depressed areas (4/17, 23.5%) than in other tumours (18/293, 6.1%; p=0.0246). KRAS, BRAF, and PIK3CA mutations were detected in 21.6%, 5.4%, and 1.0% of 310 tumours, respectively. Concomitant mutations of beta-catenin and KRAS or BRAF were detected in seven tumours. Mutation of at least one gene was detected in a significantly higher percentage of flat-type tumour tissues (75/193, 38.9%) than in protruded-type tumour tissues (25/117, 21.4%; p=0.0014), and it was correlated significantly with size (p=0.0001). In conclusion, beta-catenin mutation seemed to play an important role in flat-type tumours, especially in those with depressed areas. The genetic abnormalities could arise and accumulate in the early stage of colorectal tumourigenesis, and seem to contribute to the development of flat-type tumour.

Loss of heterozygosity in human aberrant crypt foci (ACF), a putative precursor of colon cancer

Aberrant crypt foci (ACF), the earliest neoplastic lesions of the colon, have genetic and epigenetic alterations. Loss of heterozygosity (LOH) of tumor suppressor gene loci is seen in most colon cancers, but it is not known how early in tumorigenesis this takes place. Nine microsatellite markers close to specific genes, that is, APC (5q21), PTPRJ (11p11), p53 (17p13) and DCC (18q21), were analyzed in 32 ACF and samples of normal crypts from the same 28 patients. Six losses of heterozygosity were found in 5 of 32 ACF: 4 losses of heterozygosity were at 11p11, the location of the gene for protein tyrosine phosphatase receptor type J (PTPRJ) and of a second independent region of deletion; the others were at 5q21 and 18q21. Microsatellite instability (MSI) with markers for a single locus was found in 4 of 32 ACF. All the observed allelic alterations (LOH and MSI) were in 8 of 32 ACF. The finding of LOH in ACF with normal expressions of adenomatous polyposis coli (APC) and beta-catenin proteins suggests that LOH can occur very early in colon neoplasia and perhaps even before APC mutations. The finding of 3 of 4 of the losses of heterozygosity at 11p11 for PTPRJ and half of all the losses of heterozygosity in this study at PTPRJ suggest that this gene plays a role early in colon neoplasia.

Allelic loss analysis of early-stage flat-type colorectal tumors

BACKGROUND

Flat-type colorectal tumors are rare, but are known for their unusual flat morphology and aggressive clinical behavior despite their small size. To identify distinct genetic alterations, loss of heterozygosity (LOH) analysis was performed on microdissected tissues.

MATERIALS AND METHODS

DNA was extracted from multiple microdissected foci in 43 cases of early-stage flat-type colorectal tumors and LOH analysis was performed on 2q, 4q, 5q, 12q, 14q, 15q, 17p, 18q, 18p and 22q.

RESULTS

LOH patterns were detected in one of two forms: (i) homogeneous LOH throughout the microdissected foci, which indicated the early acquisition of LOH; and (ii) heterogeneous LOH, which were detected in a part of analyzed foci. Homogeneous and heterogeneous LOH were most frequently detected on 17p (92%) followed by 18q (81%), 18p (81%), 5q (61%), 22q (51%), 14q (44%), 15q (41%), 2q (39%), 12q (36%) and 4q (32%). Homogeneous LOH was detected most frequently on 17p (68%) followed by 18p (53%), 18q (53%), 22q (34%) and 12q (27%). The average fractional allelic loss (FAL) for heterogeneous and homogeneous LOH was 0.57 and the average FAL for homogeneous LOH was 0.37.

CONCLUSIONS

Early flat-type colorectal tumors frequently shows the early occurrence of multiple LOH including 17p, 18p, 18q and 22q, which is coupled with additional LOH of other loci either simultaneously or in the early clonal progression phase. The extent and sequences of LOH may be the mechanisms responsible for the aggressive clinical behaviors of these tumors.

Loss of heterozygosity on chromosome 2 in Japanese patients with prostate cancer

BACKGROUND

Loss of heterozygosity (LOH) on chromosome 2 is thought to occur only occasionally in prostate cancer (PCa), but allelic losses in this region are frequent in other types of human cancer, such as lung, thyroid, head and neck, and cervix. Here, we show a high-resolution deletion map of markers on chromosome 2 in Japanese patients with PCa.

METHODS

Tissue samples were obtained from 66 patients with PCa. DNA from normal, tumor, or metastatic tissue was used as the template for polymerase chain reaction amplification for LOH using 24 microsatellite markers on human chromosome 2.

RESULTS

Nineteen of the 66 cases (29%) showed LOH for at least one locus on chromosome 2. LOH on 2p was observed more frequently in cancer death cases than in organ confined and regional diseases (P < 0.001). Paired DNAs were available from both primary and metastatic tumors in the eight cases of cancer death; among those pairs, we detected LOH on 2p in four primary tumors, and in all metastatic foci (P < 0.05). Detailed deletion mapping in these tumors identified four distinct commonly deleted regions on 2p 16.3, 2p 12-cent, 2q 21.3, and 2q 23.1-2q 32.1.

CONCLUSIONS

These results suggest that inactivation of putative tumor suppressor genes on chromosome 2 that may play an important role in the progression of Japanese patients with PCa.

Gene expression profiling of colorectal adenomas and early invasive carcinomas by cDNA array analysis

It is generally accepted that most colorectal carcinomas arise in pre-existing adenomas. Morphologically, colorectal adenomas can be divided into two groups, protruded type and flat type. The aim of this study was to clarify relevant alterations of gene expression associated with the early stage of colorectal carcinogenesis. Using cDNA array, we analysed the expression profiles of 550 cancer-related genes in 36 colorectal adenomas (18 flat-type and 18 protruded-type adenomas) and 14 early invasive carcinomas. Among the 550 genes, we chose 32 genes the average expression levels of which were at least three-fold up- or downregulated in tumour tissues compared with levels in matched normal tissues. A total of 13 and 19 genes were identified as up- and downregulated genes in tumour tissues, respectively. Among the upregulated genes, the average expression levels of E1AF, bone morphogenic protein (BMP)-4, insulin-like growth factor (IGF)-2, inducible nitric oxide synthase (iNOS), tissue inhibitors of metalloproteinase (TIMP)-1, Smad4, and nm23 in tumour tissues were over five times higher than those in matched normal tissues. Colorectal adenomas and early invasive carcinomas were divided into two major clusters by clustering analysis. Moreover, flat- and protruded-type adenomas were divided into two major clusters by clustering analysis. The expression profiles obtained by the cDNA array clearly indicate that colorectal adenomas and early invasive carcinomas have specific expression profiles. Likewise, the gene expression profiles of flat- and protruded-type adenomas are different. These results indicate that molecular classification of early colorectal tumours by a cDNA array is feasible.

Selective loss of codon 72 proline p53 and frequent mutational inactivation of the retained arginine allele in colorectal cancer

According to recent reports, some cancer types exhibit nonrandom allele loss at codon 72 in exon 4 of the p53 gene [coding for proline (72Pro) or arginine (72Arg)]. To clarify this phenomenon for colorectal cancer and to find out if this preferential loss might have any functional significance, p53 loss of heterozygosity (LOH) and p53 mutations were investigated in a group of 61 colorectal cancers and 28 liver metastases, and were correlated with clinicopathologic factors. A comparison of a patient's blood codon 72 status with a healthy control group did not reveal an enhanced risk of developing colorectal tumors for one of the two isoforms. p53-LOH and p53 mutations were found in 62.2% and 39.4% of primary tumors, respectively, and in 57.9% and 25% of hepatic metastases, respectively. In 14 heterozygous cases showing exon 4-LOH, only the 72Pro allele was lost and the retained 72Arg was preferentially mutated. In general, p53 mutations were significantly associated with the 72Arg tumor status (P < .001). Distal tumors showed allelic losses of the p53 gene more commonly than proximal tumors (P = .054). The prevalence of 72Arg increased in frequency with higher Dukes stage (P = .056). We suggest that either the preferential loss of 72Pro or the mutation of the 72Arg in colorectal cancer and hepatic metastases is associated with malignant potential and might reflect carcinogenic exposure, particularly in the distal part of the large intestines.

Chromosomal instability in flat adenomas and carcinomas of the colon

Flat adenomas are flat or slightly elevated dysplastic lesions of the colorectal mucosa, mostly with a tubular architecture. Compared with polypoid adenomas of similar size, flat adenomas show a higher frequency of high-grade dysplasia and rapid submucosal invasion. The aim of this study was to survey whether flat colorectal lesions differ in their pattern of chromosomal aberrations from their polypoid counterparts. Six flat adenomas and 12 flat carcinomas were analysed by comparative genomic hybridization (CGH) and the pattern of chromosomal aberrations was compared with a previously published series of 112 polypoid adenomas and 82 polypoid carcinomas. In addition, multiplex ligation-dependent probe amplification (MLPA) for identifying DNA copy number changes of 25 individual genes on chromosome 20 was performed on 14 flat and 15 polypoid tumours. With CGH, flat adenomas showed on average 1.8 gains (range 1-4) and 3.2 losses (range 0-4), and the flat carcinomas 4.5 gains (range 0-8) and 3.5 losses (range 1-6). In both adenomas and carcinomas, high frequencies of 20q gain (83% and 92%, respectively) and 18q loss (83% and 92%, respectively) were found. This correlation between 20q gain and 18q loss had previously been observed in a subgroup of polypoid colorectal tumours. Both flat and polypoid colorectal tumours with 20q gains by CGH showed similar patterns of copy number ratios for the individual genes tested. TOP1, BCL2L1, and E2F1 had median copy number ratios of 2 or higher, while ZNF217 had a ratio around 3. In conclusion, flat adenomas and carcinomas of the large intestine show a similar pattern of chromosomal aberrations to that observed in a specific subgroup of polypoid lesions. The transcription factor ZNF217 is an important candidate for driving the 20q gain.

Interaction between morphology and angiogenesis in human early colorectal cancers

Morphologically, early colorectal cancers are divided into two types: polypoid cancers and non-polypoid cancers. They vary in growth pattern, progression, and genetic alteration. Angiogenesis between polypoid and non-polypoid cancers may also be different. Therefore, the present study aims to evaluate angiogenesis in the early stages of colorectal malignancy, with particular attention to the morphological differences. The serial slides of all materials (48 polypoid cancers, 10 non-polypoid cancers, 20 adenomas and 10 normal tissues) were immunohistochemically stained for three endothelial cell markers (CD31, von Willebrand factor and CD105), counted for the number of microvessels in the same hot spots, and the angiogenic status was estimated. Polypoid cancers had higher microvessel counts and were more predominantly supplied by activated (CD105-positive, newly forming) microvessels than non-polypoid cancers. The present study indicated the possibility that the difference in growth pattern might be explained by the difference in angiogenesis between polypoid and non-polypoid cancers.

Frequent hypermethylation of RASSF1A in early flat-type colorectal tumors

Flat colorectal tumors, characterized by high-grade dysplasia from early small flat mucosal lesions, exhibit a relatively aggressive clinical behavior and are known for their infrequent K-ras mutations. In this study, we investigated the methylation status of the RASSF1A promoter in association with 3p LOH and K-ras mutations in 48 flat colorectal tumors (39 early carcinomas and nine intramucosal high-grade dysplasias). RASSF1A hypermethylation was detected in 39 of 48 (81.3%) tumors and RASSF1A methylation was also detected in 19 of 39 (49%) normal colonic mucosal tissues. 3p21.3 LOH was detected in 20 of 42 (47.6%) cases, but RASSF1 methylation was detected in cases with LOH (14 cases) and retention of 3p21.3 (20 cases). K-ras mutations were detected in seven of 48 (14.6%) tumors and the concordant occurrence of K-ras mutation and RASSF1A methylation was detected in three of 48 cases (6.3%). Overall, there was a statistically significant mutually exclusive relationship between K-ras mutations and RASSF1A methylation. In conclusion, promoter hypermethylation of RASSF1A is a frequent event and may start early in the background normal mucosa in this tumor type. An alternative cascade of abnormalities in RAS transduction pathways may be responsible for the flat morphology and aggressive nature of flat colorectal neoplasms.

Association between recurrence of sporadic colorectal cancer, high level of microsatellite instability, and loss of heterozygosity at chromosome 18q

PURPOSE

Microsatellite instability and loss of heterozygosity of chromosomes 18q, 8p, and 4p are genetic alterations commonly found in colorectal cancer. We investigated whether these genetic markers allow for the stratification of patients with Stage II to III colorectal cancer into groups with different recurrence risks, and with different prognoses.

METHODS

Tumors of 113 patients were evaluated for loss of heterozygosity of chromosomes 18q, 8p, and 4p and for microsatellite instability by use of six microsatellite markers. Genetic alterations involving each of these genetic markers were examined for association with disease recurrences and survival.

RESULTS

Loss of heterozygosity of chromosomes 18q, informative in 96 percent of cases, in Stage III tumors was associated with higher risk of overall recurrence ( P< 0.001), local recurrence ( P< 0.001), distant metastases ( P< 0.001), decreased overall survival ( P= 0.002), and disease-free survival ( P< 0.001). The recurrence rates and survival rates among patients with Stage II colorectal cancer were independent of loss of heterozygosity of chromosome 18q. Stage III and loss of heterozygosity of chromosome 8p also were associated with a higher risk of recurrences when these factors were considered individually. In multivariate analysis, only loss of heterozygosity of chromosome 18q was independently associated with risk of recurrences ( P < 0.001) and with disease-free survival ( P= 0.001). No correlation was observed between microsatellite instability and recurrence rates. However, microsatellite instability was associated with improved overall survival ( P= 0.04) and with a longer disease-free interval ( P= 0.002). Only in five cases (16.7 percent) was it possible to perform resection of recurrences; two of these patients had microsatellite instability tumor. In no cases was it possible to resect recurrence of tumors with loss of heterozygosity of chromosome 18q.

CONCLUSIONS

Loss of heterozygosity of chromosome 18q is an informative genetic marker, which in resected Stage III colorectal cancer can be used to predict recurrences and survival. Microsatellite instability identified cases that, even in the case of recurrence, have a more favorable prognosis.

Abnormal Fhit protein expression and high frequency of microsatellite instability in sporadic colorectal cancer

The role of Fhit protein in the oncogenesis of colorectal cancer is still in debate. Recent studies have revealed that reduced Fhit protein expression is associated with a deficiency of the mismatch repair protein. One hundred and twenty unselected patients who underwent curative resection for sporadic colorectal cancer in a three-year period were evaluated for microsatellite instability (MSI) using six microsatellite markers, and for the presence of Fhit and mismatch repair (MMR) proteins (Mlh1 and Msh2) by means of immunostaining. The relations between these markers were analysed. Reduced or absent Fhit expression was noted in 18 out of 118 patients. This altered expression was significantly higher in right-sided cancer (P = 0.005), mucinous tumours (P = 0.005) and in poorly differentiated histological types (P = 0.0001). MSI was found in 22 out of 109 patients, more so in right-sided cancer (P = 0.0001), poorly differentiated histology (P = 0.0001), and mucinous tumours (P = 0.0001). No association was found with TNM stage. MSI was present in 66.7% of tumours with altered Fhit expression and in only 10% of tumours with preserved or intermediate Fhit expression (P = 0.0001). Of the tumours with reduced or absent Fhit expression, 72.2% had loss of nuclear Mlh1 or Msh2 expression compared with only 14% of the preserved or intermediate Fhit expression tumours (P = 0.0001). These results support the hypothesis that deficiency in a MMR gene could be a cause of the high frequency of alterations in Fhit expression, and they permit the suggestion that FHIT gene alteration may be part of the genetic pathway involving MSI through which some colorectal cancers arise.

Analysis of genetic alterations, classified according to their DNA ploidy pattern, in the progression of colorectal adenomas and early colorectal carcinomas

DNA aneuploidy is a biological marker of the oncogenic potential of colorectal adenomas. The accumulation of genetic alterations of cancer-related genes is also essential for colorectal carcinogenesis. However, it is unclear whether there is any relationship between these genetic alterations and the DNA ploidy of colon tumour cells in the progression of colorectal adenomas and early colorectal carcinomas. Here we have studied the DNA ploidy state and genetic alterations occurring in colorectal tumours using the crypt isolation technique. Crypts isolated from a total of 106 colorectal tumors (adenoma, 93; early carcinoma, 13) were examined using a combination of flow cytometric analysis of DNA content, polymerase chain reaction-microsatellite assay, and single-strand conformation polymorphism assay for evidence of chromosomal allelic imbalance (AI; 17p; 5q; 18q) or p53 gene mutation. In addition, we examined microsatellite instability (MSI) with BAT 26 primer sets. DNA multiploidy was infrequently detected in colorectal adenomas (15.1%), in contrast to early carcinomas (46.2%). There was a significant difference in the incidence of AI of chromosome 18q between diploid adenomas and aneuploid populations of multiploid adenomas (18.1% vs 57.1%, p = 0.0043). Mutation of p53 was also found more frequently in aneuploid populations of early multiploid colorectal carcinomas than in early diploid colorectal carcinomas (66.7% vs 0%, p = 0.021). MSI was found in only 2 of 93 adenomas, with no MSI detected in early colorectal cancers. The two MSI-positive adenomas were diploid. We subdivided multiploid adenomas into two groups: those with a low or a high DNA index (DI). The incidence of genetic alterations of high-DI adenomas did not differ from those of low-DI adenomas. Allelic imbalance involving loci on chromosome 18q and mutations of p53 seems to be associated with the progression of diploidy to multiploidy in colorectal tumours. On the other hand, MSI may be associated with the development of some diploid tumours. In addition, the incidence of genetic alterations in the colorectal adenomas that we examined appears to be independent of the tumour's DNA index.

Variation in MT expression in early-stage depressed-type and polypoid-type colorectal tumours

Metallothionein (MT) expression is observed in various carcinomas, but its role is not fully understood. To clarify the clinicopathological significance of MT, 87 colorectal adenomas and 128 early-stage carcinomas were immunohistochemically analysed for MT expression. The degree of MT immunostaining of a specimen was graded according to the proportion of MT-positive cells; negative (<5%) and positive (focally 5-50%, diffusely >50%). MT expression significantly decreased with tumour development. For carcinomas, MT-positivity was significantly associated with depth of invasion (T1 60% versus T2 33%; P<0.01), vascular involvement (positive 35% versus negative 61%; P<0.01) and morphology (polypoid 62% versus depressed 26%; P<0.01). Regarding MT-positive distribution, the diffuse-positive rate in MT-positive polypoid lesions was 28%, while MT-positive depressed lesions were all diffusely stained (P<0.01). In conclusion, our results suggested that decreasing MT expression is an early event in colorectal carcinogenesis and may reflect local invasion. Furthermore, MT-positive distribution may reflect genetic differences between the polypoid and depressed-type.

Loss of heterozygosity in the clonal evolution of flat colorectal neoplasms

In contrast to invasive colorectal carcinomas that develop in typical exophytic adenoma-carcinoma sequences, some invasive cancers may evolve from flat mucosal dysplastic lesions. Despite their relatively small size, these flat colorectal lesions are often associated with high-grade dysplasia and may show an aggressive clinical course. To delineate the genetic pathways in the clonal evolution of these tumors, multiple foci were microdissected from 13 cases and the allelic deletions of 15 chromosomal arms were analysed. Loss of heterozygosity (LOH) was detected most frequently on 17p (77%), followed by 18q (69%), and 5q (54%). In five cases with concomitant low-grade adenomas, only one case showed LOH in low-grade adenoma foci. In high-grade dysplasia with/without submucosal invasion, early and homogeneous LOH of one to several chromosomal arms was detected. Overall, homogeneous and thus early LOH were most frequently detected on 17p (seven of 10 cases with 17p LOH), followed by 3p (two of three cases with 3p LOH), and 5q (four of seven cases with 5q LOH). In addition to homogeneous LOH, the LOH patterns observed in different portions of dysplasias and invasive cancers in individual cases identified several different genetic patterns of tumour progression, either with linear or branching (divergent) trees. Positive immunostaining for p53 was detected in 10 of the 13 cases; of these, five cases were concomitant with 17p LOH in all of the microdissected foci, four cases were concomitant with 17p LOH in a majority of foci and, one case showed retention of 17p. Except for the flat configuration and early 17p LOH, genetic heterogeneity in the flat high-grade dysplastic foci was found to be similar to genetic chaos in the late dysplastic and preinvasive stages of exophytic adenoma. These findings suggest a potentially aggressive course for these neoplasms.

Analysis of Ki-ras gene mutations associated with DNA diploid, aneuploid, and multiploid colorectal carcinomas using a crypt isolation technique

BACKGROUND AND AIM

Current evidence suggests a possible relationship between DNA ploidy status and Ki-ras gene mutations in human cancers. However, the conventional method does not enable accurate determination of DNA ploidy status of a tumor cell. The present study attempts to clarify whether Ki-ras gene mutations are associated with DNA ploidy status in sporadic colorectal carcinomas using a crypt isolation technique coupled with DNA cytometric sorting.

METHODS

Polymerase chain reaction and single-strand conformation polymorphism and direct sequencing were used to analyze Ki-ras gene mutations in 82 sporadic colorectal carcinomas: 21 diploid, 12 aneuploid, and 49 multiploid. In addition, microsatellite instability (MSI) was assessed using seven microsatellite markers to study the relationship to Ki-ras mutations.

RESULTS

Ki-ras mutations were found in 12 of 21 diploid carcinomas and in 8 of 12 aneuploid carcinomas. In contrast, Ki-ras gene mutations were detected infrequently in the 34 multiploid carcinomas examined, 8 of which were seen in diploid populations and 10 in aneuploid populations. On the other hand, Ki-ras gene mutations were inversely correlated with MSI, which was found in diploid carcinomas only.

CONCLUSIONS

The low frequency of Ki-ras gene mutations that we observed in multiclonal colorectal carcinomas suggests that development of multiclonal colorectal carcinoma may involve a mechanism different from that involved in the development of diploid or aneuploid colorectal carcinomas.

Molecular disorders in transitional vs. peripheral zone prostate adenocarcinoma

Loss of heterozygosity (LOH) and microsatellite instability (MSI) have been shown to be mechanisms for tumor-suppressor gene inactivation in human oncogenesis. In our study, we examined LOH and MSI using 16 polymorphic markers of DNA for chromosomes 1, 3, 7, 8, 10 and 11. Microdissected tumor samples were isolated from 32 patients, representing 11 foci of incidentally discovered prostate cancer of the transitional zone (TZ), 12 prostate cancer of the peripheral zone (PZ) and 10 of high-grade PIN. We found loss of heterozygosity in the TZ group in 91% of informative cases (10/11) with al least 1 marker compared to 58% of cases (7/12) in PZ group and 70% of cases (7/10) in the HGPIN group. Chromosome 7 showed the highest rate of allelic loss in all 3 categories, with loss of 43% of loci in PIN, 37% in TZ tumors and 31% in PZ tumors. At chromosome 11, LOH was detected in 26% of loci in the TZ group, in 7% of loci in the PZ group and in 13% of loci in the PIN group. On chromosome 8, the PZ and HGPIN group showed allelic loss in 22% and 21% of loci, respectively, compared to 10% detected in the TZ group. The TZ group showed a significant higher rate of allelic instability compared to that observed in tumor samples from the peripheral zone: 73% of cases (8/11) showed genetic alterations (RER+ phenotype) in at least 4 loci analyzed compared to 8% and 10% in the PZ and HGPIN groups, respectively (p = 0.0006). These data suggest that transitional zone carcinoma and peripheral zone carcinoma display distinct and specific genetic alterations in different chromosomes. This diversity may help explain biologic and clinical differences between carcinomas arising in these distinct zones of the prostate. Also our results strongly suggest that the RER+ mutator phenotype could be linked to early development of transitional zone prostate carcinoma.

Glut1 expression in T1 and T2 stage colorectal carcinomas: its relationship to clinicopathological features

Glucose uptake is mediated by glucose transporter (Glut) proteins, which exhibit altered expression in a variety of malignant neoplasms. Glut1 expression is thought to be a potential marker for malignant transformation. The aim of the present study was to investigate the expression of Glut1 protein in colorectal adenomas, T1 and T2 stage carcinomas. Immunohistochemical detection of Glut1 protein was examined in 141 formalin-fixed and paraffin-embedded colorectal tumour specimens (57 adenomas, 84 carcinomas). The degree of Glut1 immunostaining of a specimen was graded according to the proportion of Glut1-positive cells in it; absent (positive cells are 0%), weakly positive (less than 10%), moderately positive (10-50%), and strongly positive (more than 50%). Glut1 expression was present in 18% of the adenomas with low-grade dysplasia, and in 63% of the adenomas with high-grade dysplasia. The positivity in such lesions was usually weak, but was moderate in 8% of the adenomas with high grade dysplasia. For the carcinomas, there were significant correlations between Glut1-positivity and depth of invasion (T1 45% versus T2 74%, P<0.01), histological differentiation (well 49% versus moderately to poorly 74%, P< 0.05) and morphological type (polypoid 42% versus depressed 73%, P< 0.05), if the cut-off value was set at 10% of cells. In conclusion, we clarified the relationship between Glut1 expression and clinicopathological features in T1 and T2 stage colorectal carcinomas, and our results suggested a high malignant potential of the depressed-type carcinoma.

Genetic alterations in DNA diploid, aneuploid and multiploid colorectal carcinomas identified by the crypt isolation technique

Loss of heterozygosity (LOH) and microsatellite instability (MSI) commonly occur in colorectal carcinomas. However, the role of these genetic alterations in determining DNA ploidy status of tumors (diploid, aneuploid and multiploid) remains unclear. In the present study, we attempted to clarify the relationship between genetic alterations and DNA ploidy status. Crypt isolation coupled with DNA cytometric sorting and polymerase chain reaction assay (17 microsatellite markers) were used to study allelic losses and MSI in 59 colorectal carcinomas (diploid, 15; aneuploid, 10 and multiploid, 34). Of the 15 diploid carcinomas, 6 exhibited MSI in which allelic losses were rarely found. The other 9 diploid tumors mostly exhibited allelic losses, but none displayed MSI status. Whereas allelic losses frequently occurred in the aneuploid carcinomas and the aneuploid populations of multiploid carcinomas, they were rarely detected in the diploid populations of multiploid carcinomas. MSI status was not observed in aneuploid carcinomas nor in either population of multiploid carcinomas. Although multiploid carcinomas genetically resemble aneuploid carcinomas in the expression of the severe LOH phenotype, the genetic alterations seen in the diploid populations of multiploid carcinomas may differ from those of diploid carcinomas. Furthermore, all diploid, aneuploid and both the diploid and aneuploid fractions of the multiploid tumors that were non-MSI exhibited a high rate of LOH, suggesting that LOH is independent of the tumor's ploidy status.

Localization of a novel tumor metastasis suppressor region on the short arm of human chromosome 2

Much of the lethality of malignant neoplasms is attributable directly to their ability to develop secondary growths in organs at a distance from the primary tumor mass, whereas few patients die from their primary neoplasm. Little is known about the molecular mechanism of tumor metastasis, however, which is controlled by a variety of positive and negative factors. In the search for metastasis suppressor genes, we have used the microcell-mediated chromosome transfer method and a rat prostate tumor model in SCID mice. When human chromosome 2 was introduced into the highly metastatic rat prostatic tumor cell, AT6.1, the metastatic ability of this cell was significantly (>99%) decreased in animals. An STS-based PCR analysis for 8 hybrid clones indicates that the suppressor activity is located in the p25-22 region of the chromosome. Furthermore, the AT6.1 cell with human chromosome 2 showed a reduced ability to invade Matrigel, suggesting that the suppressor activity is involved in the step of tumor invasion during the progression of prostate cancer. We have also examined the status of the suppressor region on chromosome 2 in human prostate cancer specimens and found that this region was often lost in high-grade tumors. These results suggest that the putative suppressor gene on chromosome 2 is functionally involved in the progression of human prostate cancer. Genes Chromosomes Cancer 28:285-293, 2000.

Loss of heterozygosity in human skin

Loss of heterozygosity (LOH) is a genetic mechanism by which a heterozygous somatic cell becomes either homozygous or hemizygous because the corresponding wild-type allele is lost. LOH has today been recognized as a major cause of malignant growth. This article gives a comprehensive review of skin disorders in which an origin from LOH has been either documented at the molecular level or postulated on the basis of clinical evidence. LOH has been shown to cause basal cell carcinoma, squamous cell carcinoma, and malignant melanoma, but this mechanism can likewise be taken as an important model to explain the origin of many other skin diseases such as benign hamartomas; type 2 segmental manifestation of autosomal dominant skin disorders; a pronounced segmental manifestation of acquired skin disorders with a polygenic background, superimposed on symmetric lesions of the usual type; paired mutant patches in the form of either allelic or nonallelic twin spotting; and the exceptional familial occurrence of some nevi, reflecting paradominant transmission. completion of this learning activity, readers should be familiar with the mechanism of LOH and its general significance for the biology of plants, animals, and humans. Participants should understand that this mechanism plays a crucial role not only in cutaneous malignant growth but also in the development of benign skin disorders, and they should be able to examine such diseases with a prepared mind to gain a better understanding of their origin.