Infrequent mutation of the tumour-suppressor gene Smad4 in early-stage colorectal cancer

S100A2 induces epithelial-mesenchymal transition and metastasis in pancreatic cancer by coordinating transforming growth factor β signaling in SMAD4-dependent manner

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive tumor and is associated with a poor prognosis. Treatment strategies for PDAC are largely ineffective primarily because of delay in its diagnosis and limited efficacy of systematic treatment. S100A2 is associated with the proliferation, migration, and differentiation of several tumors; however, its effects on PDAC and the associated molecular mechanisms remain to be explored. We studied the mechanisms underlying the effect of S100A2 on epithelial-mesenchymal transition (EMT) and metastasis in PDAC cells. We found that the level of S100A2 remarkably increased and was associated with poor PDAC prognosis. The overexpression of S100A2 in PANC-1 cells also induced EMT, in addition to increasing the invasion and migration of PDAC cells, whereas the knockdown of S100A2 markedly inhibited cell metastasis. Furthermore, S100A2 was found to enhance metastatic abilities in vivo. The overexpression of S100A2 increased SMAD4 expression, whereas the knockdown of S100A2 reduced SMAD4 expression. SMAD4 overexpression could effectively rescue the effects of S100A2 knockdown on EMT. S100A2 mechanistically activated the transforming growth factor (TGF)-β/Smad2/3 signaling pathway, upregulated SMAD4 expression, induced EMT, and increased PANC-1 cell metastasis. In conclusion, the S100A2/SMAD4 axis modulates EMT to accelerate PDAC development. Our results supplement and enrich the understanding of the pathogenesis underlying PDAC and provide a new theoretical basis and strategy targeting S100A2 for the diagnosis and treatment of PDAC.

Multiple roles of mothers against decapentaplegic homolog 4 in tumorigenesis, stem cells, drug resistance, and cancer therapy

The transforming growth factor (TGF)-β signaling pathway controls many cellular processes, including proliferation, differentiation, and apoptosis. Abnormalities in the TGF-β signaling pathway and its components are closely related to the occurrence of many human diseases, including cancer. Mothers against decapentaplegic homolog 4 (Smad4), also known as deleted in pancreatic cancer locus 4, is a typical tumor suppressor candidate gene locating at q21.1 of human chromosome 18 and the common mediator of the TGF-β/Smad and bone morphogenetic protein/Smad signaling pathways. It is believed that Smad4 inactivation correlates with the development of tumors and stem cell fate decisions. Smad4 also interacts with cytokines, miRNAs, and other signaling pathways, jointly regulating cell behavior. However, the regulatory function of Smad4 in tumorigenesis, stem cells, and drug resistance is currently controversial. In addition, Smad4 represents an attractive therapeutic target for cancer. Elucidating the specific role of Smad4 is important for understanding the mechanism of tumorigenesis and cancer treatment. Here, we review the identification and characterization of Smad4, the canonical TGF-β/Smad pathway, as well as the multiple roles of Smad4 in tumorigenesis, stem cells, and drug resistance. Furthermore, we provide novel insights into the prospects of Smad4-targeted cancer therapy and the challenges that it will face in the future.

Investigating the utility of extended mutation analysis in gastrointestinal peritoneal metastasis

BACKGROUND AND OBJECTIVES

Outcomes for gastrointestinal peritoneal metastases (GI-PM) are worse compared to systemic metastases, with a paucity of data exploring extended mutation profiling. An exploratory mutation analysis in GI-PMs was performed as a "proof of concept" of potential predictive values of profiling in GI-PM and rates of actionable mutations.

METHODS

The study included 40 GI-PM patients: 14 low-grade mucinous carcinoma peritonei and 26 HG-PM (12 colons, 10 appendix, 4 small bowels). Demographics, histologies, peritoneal cancer indexes, cytoreduction scores, and survival data were collected. NGS 50-gene mutation profiling was performed on 38 specimens. The association of mutations with survival was evaluated in high-grade PM.

RESULTS

KRAS, TP53, and SMAD4 mutations were observed in 61%, 29%, and 8% of cases across all tumor histologies. In 66% cases >1 mutations occurred, associated with decreased survival in HG-PM: 32 vs 73 months, P = .03. TP53 or SMAD4 mutations were associated with decreased survival in HG-PM: 22 vs 48 months, P = .02. Actionable mutations were detected in 70%.

CONCLUSION

Actionable mutations were detected at high rates. GI-PMs have similar mutational profiles and TP53, SMAD4, and/or >1 mutation were associate with decreased survival in HG-PM. This data supports the concept of the extended mutation profiling utility in GI-PM warranting further investigation.

Genetic variant of TMBIM1 is associated with the susceptibility of colorectal cancer in the Chinese population

BACKGROUND AND AIMS

Recent meta-analysis of genome-wide association studies (GWASs) identified a novel variant rs992157 at 2q35 that was associated with colorectal cancer (CRC) in the population of European ancestry. We aimed to replicate the association of rs992157 with CRC in the Chinese population and to further determine the real susceptible gene of CRC as indicated by this variant.

METHODS

824 CRC patients and 1063 healthy controls were included. The frequency of the genotype and the allele of rs992157 were compared between the patients and the controls and between different subgroups of patients classified by status of metastasis. Expression level of TMBIM1 was compared between the tumor tissue and the adjacent normal tissues collected from 43 patients during surgery. Besides, the relationship between genotypes of rs992157 and the tissue expression of TMBIM1 was analyzed.

RESULTS

Patients were found to have significantly higher frequency of allele G than the controls (44.2% vs. 40.0%, P = 0.009; OR = 1.18). Moreover, allele G was associated with an increased risk of lymph node metastasis (P = 0.02) and distant metastasis of CRC (P = 0.04). The mean expression level of TMBIM1 was significantly higher in tumor tissue than in the adjacent normal tissues (0.0019 ± 0.00068 vs. 0.00041 ± 0.00024, P < 0.001). In addition, patients with genotype GG were found to have remarkably higher TMBIM1 expression in the tumors than those with genotype AA (0.0024 ± 0.00052 vs. 0.0015 ± 0.00078, P = 0.005).

CONCLUSION

Variant rs992157 is significantly associated with the susceptibility and progression of CRC. It can increase the risk of CRC possibly via up-regulation of TMBIM1.

The role of TGF-β/SMAD4 signaling in cancer

Transforming growth factor β (TGF-β) signaling pathway plays important roles in many biological processes, including cell growth, differentiation, apoptosis, migration, as well as cancer initiation and progression. SMAD4, which serves as the central mediator of TGF-β signaling, is specifically inactivated in over half of pancreatic duct adenocarcinoma, and varying degrees in many other types of cancers. In the past two decades, multiple studies have revealed that SMAD4 loss on its own does not initiate tumor formation, but can promote tumor progression initiated by other genes, such as KRAS activation in pancreatic duct adenocarcinoma and APC inactivation in colorectal cancer. In other cases, such as skin cancer, loss of SMAD4 plays an important initiating role by disrupting DNA damage response and repair mechanisms and enhance genomic instability, suggesting its distinct roles in different types of tumors. This review lists SMAD4 mutations in various types of cancer and summarizes recent advances on SMAD4 with focuses on the function, signaling pathway, and the possibility of SMAD4 as a prognostic indicator.

Progression inference for somatic mutations in cancer

Computational methods were employed to determine progression inference of genomic alterations in commonly occurring cancers. Using cross-sectional TCGA data, we computed evolutionary trajectories involving selectivity relationships among pairs of gene-specific genomic alterations such as somatic mutations, deletions, amplifications, downregulation, and upregulation among the top 20 driver genes associated with each cancer. Results indicate that the majority of hierarchies involved TP53, PIK3CA, ERBB2, APC, KRAS, EGFR, IDH1, VHL, etc. Research into the order and accumulation of genomic alterations among cancer driver genes will ever-increase as the costs of nextgen sequencing subside, and personalized/precision medicine incorporates whole-genome scans into the diagnosis and treatment of cancer.

Association of SMAD4 mutation with patient demographics, tumor characteristics, and clinical outcomes in colorectal cancer

SMAD4 is an essential mediator in the transforming growth factor-β pathway. Sporadic mutations of SMAD4 are present in 2.1-20.0% of colorectal cancers (CRCs) but data are limited. In this study, we aimed to evaluate clinicopathologic characteristics, prognosis, and clinical outcome associated with this mutation in CRC cases. Data for patients with metastatic or unresectable CRC who underwent genotyping for SMAD4 mutation and received treatment at The University of Texas MD Anderson Cancer Center from 2000 to 2014 were reviewed. Their tumors were sequenced using a hotspot panel predicted to cover 80% of the reported SMAD4 mutations, and further targeted resequencing that included full-length SMAD4 was performed on mutated tumors using a HiSeq sequencing system. Using The Cancer Genome Atlas data on CRC, the characteristics of SMAD4 and transforming growth factor-β pathway mutations were evaluated according to different consensus molecular subtypes of CRC. Among 734 patients with CRC, 90 (12%) had SMAD4 mutations according to hotspot testing. SMAD4 mutation was associated with colon cancer more so than with rectal cancer (odds ratio 2.85; p<0.001), female sex (odds ratio 1.71; p = 0.02), and shorter overall survival than in wild-type SMAD4 cases (median, 29 months versus 56 months; hazard ratio 2.08; p<0.001 [log-rank test]). SMAD4 mutation was not associated with age, stage at presentation, colonic location, distant metastasis, or tumor grade. A subset of patients with metastatic CRC (n = 44) wild-type for KRAS, NRAS, and BRAF who received anti-epidermal growth factor receptor therapy with mutated SMAD4 (n = 13) had shorter progression-free survival duration than did patients wild-type for SMAD4 (n = 31) (median, 111 days versus 180 days; p = 0.003 [log-rank test]). Full-length sequencing confirmed that missense mutations at R361 and P356 in the MH2 domain were the most common SMAD4 alterations. In The Cancer Genome Atlas data, SMAD4 mutation frequently occurred with KRAS, NRAS, and BRAF mutations and was more common in patients with the consensus molecular subtype 3 of CRC than in those with the other 3 subtypes. This is one of the largest retrospective studies to date characterizing SMAD4 mutations in CRC patients and demonstrates the prognostic role and lack of response of CRC to anti-epidermal growth factor receptor therapy. Further studies are required to validate these findings and the role of SMAD4 mutation in CRC.

Clinicopathological and genetic differences between low-grade and high-grade colorectal mucinous adenocarcinomas

BACKGROUND

Although colorectal mucinous adenocarcinomas (MCs) are conventionally regarded as exhibiting high-grade differentiation, they can be divided by differentiation into 2 groups according to the glandular appearance: low-grade mucinous adenocarcinoma (low-MC) and high-grade mucinous adenocarcinoma (high-MC).

METHODS

Patients with colorectal cancer (CRC) who underwent surgical resection between 2000 and 2012 were enrolled in this study. Among the cases with MC, the clinicopathological and genetic differences between low-MC and high-MC were investigated with next-generation sequencing.

RESULTS

A total of 1373 patients with CRC were analyzed. Forty patients (2.9%) had MC, and 13 patients had high-MC. Patients with MC had significantly shorter disease-free survival (DFS) and overall survival (OS) periods than those with nonmucinous carcinoma. When low-MC patients and high-MC patients were compared, those with high-MC had significantly shorter DFS and OS periods than those with low-MC. Multivariate analyses revealed that high-MC was significantly associated with both shorter DFS and shorter OS, but low-MC was not. A genome analysis revealed that low-MC had a considerably larger number of mutations than high-MC, and Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations and adenomatous polyposis coli mutations were particularly frequently found in low-MC. In contrast, SMAD family member 4 (SMAD4) mutations were frequently found in high-MC.

CONCLUSIONS

High-MC is an independent prognostic factor in CRC (but low-MC is not), and it is genetically different from other CRCs, including low-MC. Both the clinicopathological differences and the genetic differences suggest that low-MC and high-MC should be distinguished in clinical settings.

SMAD2, SMAD3 and SMAD4 mutations in colorectal cancer

Activation of the canonical TGF-β signaling pathway provides growth inhibitory signals in the normal intestinal epithelium. Colorectal cancers (CRCs) frequently harbor somatic mutations in the pathway members TGFBR2 and SMAD4, but to what extent mutations in SMAD2 or SMAD3 contribute to tumorigenesis is unclear. A cohort of 744 primary CRCs and 36 CRC cell lines were sequenced for SMAD4, SMAD2, and SMAD3 and analyzed for allelic loss by single-nucleotide polymorphism (SNP) microarray analysis. Mutation spectra were compared between the genes, the pathogenicity of mutations was assessed, and relationships with clinicopathologic features were examined. The prevalence of SMAD4, SMAD2, and SMAD3 mutations in sporadic CRCs was 8.6% (64 of 744), 3.4% (25 of 744), and 4.3% (32 of 744), respectively. A significant overrepresentation of two genetic hits was detected for SMAD4 and SMAD3, consistent with these genes acting as tumor suppressors. SMAD4 mutations were associated with mucinous histology. The mutation spectra of SMAD2 and SMAD3 were highly similar to that of SMAD4, both in mutation type and location within the encoded proteins. In silico analyses suggested the majority of the mutations were pathogenic, with most missense changes predicted to reduce protein stability or hinder SMAD complex formation. The latter altered interface residues or disrupted the phosphorylation-regulated Ser-Ser-X-Ser motifs within SMAD2 and SMAD3. Functional analyses of selected mutations showed reductions in SMAD3 transcriptional activity and SMAD2-SMAD4 complex formation. Joint biallelic hits in SMAD2 and SMAD3 were overrepresented and mutually exclusive to SMAD4 mutation, underlining the critical roles of these three proteins within the TGF-β signaling pathway.

Expression of deleted in pancreatic carcinoma locus 4 and transforming growth factor-β1 in human colorectal carcinoma and their clinical significance

AIM: To investigate the expression of deleted in pancreatic carcinoma locus 4 (DPC4) and transforming growth factor-β1 (TGF-β1) in human colorectal cancer tissues and their clinical significances.

METHODS: Forty-eight samples of human colorectal carcinoma were collected from patients from January 2005 to December 2005. In situ hybridization and immunohistochemistry were used to detect DPC4/TGF-β1 mRNA and protein expression respectively.

RESULTS: The expression of DPC4 mRNA was lower in colorectal carcinoma specimens as compared with that in normal colorectal specimens (52.1% vs 72.9%, P < 0.01), while TGF-β1 mRNA expression was higher in carcinoma specimens (68.8% vs 41.7%, P < 0.01). The level of DPC4 protein expression in the cancer specimens was significantly lower than that in the normal specimens, while TGF-β1 protein level were higher in the carcinoma specimens. DPC4 expression was related with the tumor size, clinical stages, differentiation degree and lymph node metastasis, while TGF-β1 expression was related with the clinic stage, differentiation degree and lymph node metastasis. There existed a close correlation between DPC4 and TGF-β1 expression (χ² = 3.95, P < 0.05).

CONCLUSION: DPC4 and TGF-β1 are the capital factors in TGF-β transduction pathway. Low-expression of DPC4 and over-expression of TGF-β1 may serve as an index for unfavorable prognosis of colorectal carcinoma.

Transforming growth factor-beta pathway disruption and infiltration of colorectal cancers by intraepithelial lymphocytes

AIMS

Colorectal cancers deficient in DNA mismatch repair (MMR) are often characterized by the presence of numerous intraepithelial lymphocytes (IELs). These CD8+ T cells selectively express CD103, which is upregulated locally by transforming growth factor (TGF)-beta, and adhere to E-cadherin expressed by mucosal epithelia. Many of these cancers also possess inactivating mutations in the type II TGF-beta receptor and are believed to be insensitive to TGF-beta. The present study aimed to explore whether such refractoriness to TGF-beta is an independently contributing factor to IEL retention.

METHODS AND RESULTS

A panel of colorectal cancers enriched for DNA MMR deficiency was examined by immunohistochemistry to explore the expression levels and localization of various components in the TGF-beta signalling pathway. Logistic regression was then carried out in order to identify predictors of elevated lymphocytic infiltration independent of DNA MMR status. Increases in Smad4 expression, tumour cell proliferation and TGF-beta secretion each emerged as independent predictors of marked lymphocyte infiltration.

CONCLUSIONS

These results strongly support the hypothesis that refractoriness to normal TGF-beta signalling in colorectal cancers plays a role in the retention of lymphocytes within tumour epithelium. Since IEL infiltration is an independent predictor of favourable prognosis, the TGF-beta pathway may represent an important therapeutic target.

Refining molecular analysis in the pathways of colorectal carcinogenesis

BACKGROUND & AIMS

In the stepwise model, specific genetic and epigenetic changes accumulate as colorectal adenomas progress to carcinomas (CRCs). CRCs also acquire global phenotypes, particularly microsatellite instability (MSI) and aneuploidy/polyploidy (chromosomal instability, CIN). Few changes specific to MSI-low or CIN+ cancers have been established.

METHODS

We investigated 100 CRCs for: mutations and loss of heterozygosity (LOH) where appropriate, of APC, K-ras, BRAF, SMAD4, and p53; deletion on 5q around APC and 18q around SMAD4; total chromosomal-scale losses and gains; MSI; and CIN.

RESULTS

As expected, CIN- cancers had fewer chromosomal changes overall than CIN+ lesions, but after correcting for this, 5q deletions alone predicted CIN+ status. 5q deletions were not, however, significantly associated with APC mutations, which were equally frequent in CIN+ and CIN- tumors. We therefore found no evidence to show that mutant APC promotes CIN. p53 mutations/LOH were more common in CIN+ than CIN- lesions, and all chromosomal amplifications were in CIN+ tumors. CIN- cancers could be subdivided according to the total number of chromosomal-scale changes into CIN-low and CIN-stable groups; 18q deletion was the best predictor, being present in nearly all CIN-low lesions and almost no CIN-stable tumors. MSI-low was not associated with CIN, any specific mutation, a mutational signature, or clinicopathologic characteristic.

CONCLUSIONS

Overall, the components of the stepwise model (APC, K-ras, and p53 mutations, plus 18q LOH) tended to co-occur randomly. We propose an updated version of this model comprising 4 pathways of CRC pathogenesis, on the basis of 5q/18q deletions, MSI (high/low), and CIN (high/low/stable).

Loss of Heterozygosity on Chromosome 10p14–p15 in Colorectal Carcinoma

High frequencies of loss of heterozygosity (LOH) on chromosome 10p14-p15 have been reported in various tumors, including gliomas, pulmonary carcinoid tumors and cervical, hepatic, prostatic and esophageal carcinomas. However, LOH on chromosome 10p14-p15 in colorectal tumors has not been reported. Therefore, we examined LOH on chromosome 10p14-p15 in 60 colorectal carcinomas (21 superficial and 39 advanced types) by microsatellite assay. Three microsatellite loci, D10S191 (10p14), D10S558 and D10S249 (10p15) were examined by polymerase chain reaction [early colorectal carcinomas, LOH of markers D10S191 (36%), D10S558 (7%) and D10S249 (11%), and in advanced colorectal carcinomas, LOH of markers D10S191 (20%), D10S558 (13%) and D10S249 (33%)]. There were no significant associations between LOH on chromosome 10p14-p15 and clinicopathologic features, including patient age, sex, tumor location, depth of invasion, histologic type, lymph node metastasis and prognosis. These data suggest that a putative tumor suppressor gene associated with colorectal carcinogenesis may be located on chromosome 10p14-p15 and that alteration of this gene may be involved in the development but not progression of colorectal tumors.

Analysis of SMAD4/DPC4 gene alterations in multiploid colorectal carcinomas

BACKGROUND

Although recent animal studies have shown that SMAD4/DPC4 gene alterations are essential for late-stage intestinal tumorigenesis, the role of SMAD4/DPC4 gene alterations in primary human colorectal carcinomas is not fully understood. Therefore, we attempted to clarify the role of the SMAD4/DPC4 gene during tumor progression of colorectal carcinoma.

METHODS

Differences in allelic imbalance (AI) and mutations of the SMAD4/DPC4 gene between diploid and aneuploid populations were analyzed for 30 sporadic DNA multiploid colorectal carcinomas (used as a tumor progression model and defined as the coexistence of diploid and aneuploid cells within the same tumor). The crypt isolation technique was coupled with DNA cytometric sorting and a polymerase chain reaction assay. In addition, hypermethylation of the promoter region was examined to clarify whether inactivation of gene expression occurred.

RESULTS

Although a SMAD4/DPC4 gene AI was detected in only 5 of 27 informative diploid populations, 25 of 27 aneuploid populations had a SMAD4/DPC4 gene AI. Mutation of the SMAD4/DPC4 gene was detected in only one aneuploid population of multiploid colorectal carcinomas, but not in the corresponding diploid population. In total, 20 available multiploid carcinomas were selected for methylation analysis, and no evidence of hypermethylation of the promoter region was found.

CONCLUSIONS

We suggest that, although mutation of the SMAD4/DPC4 gene and hypermethylation of the promoter region are infrequent events in colorectal tumorigenesis, AI at the SMAD4/DPC4 gene locus may play a key role in the progression of colorectal carcinomas.

Pathogenesis and risk factors of small bowel adenocarcinoma: a colorectal cancer sibling?

Small bowel adenocarcinoma (SBA) is a very rare entity accounting for one-fourth of the small intestine neoplasms. Usually accompanied by nonspecific symptoms occurring late in the course of the disease, they are associated with a dismal prognosis. It appears that SBA shares several genetic characteristics with large bowel tumors, but also has unique features. The purpose of this article is to review pathogenesis and risks factors of SBA to better understand its molecular features as well as its resemblances and dissimilarities with colorectal cancer (CRC). Better understanding of sporadic and hereditary genetic pathways potentially involved will undoubtedly lead to better prevention and therapeutic management of this rare but aggressive disease.

The role of Fas ligand and transforming growth factor beta in tumor progression: molecular mechanisms of immune privilege via Fas-mediated apoptosis and potential targets for cancer therapy

Despite the fact that expression of Fas ligand (FasL) in cytotoxic T lymphocytes (CTLs) and in natural killer (NK) cells plays an important role in Fas-mediated tumor killing, During tumor progression FasL-expressing tumor cells are involved in counterattacking to kill tumor-infiltrating lymphocytes (TILs). Soluble FasL levels also increase with tumor progression in solid tumors, and this increase inhibits Fas-mediated tumor killing by CTLs and NK cells. The increased expression of FasL in tumor cells is associated with decreased expression of Fas; and the promoter region of the FASL gene is regulated by transcription factors, such as neuronal factor kappaB (NF-kappaB) and AP-1, in the tumor microenvironment. Although the ratio of FasL expression to Fas expression in tumor cells is not strongly related to the induction of apoptosis in TILs, increased expression of FasL is associated with decreased Fas levels in tumor cells that can escape immune surveillance and facilitate tumor progression and metastasis. Transforming growth factor beta (TGF-beta) is a potent growth inhibitor and has tumor-suppressing activity in the early phases of carcinogenesis. During subsequent tumor progression, the increased secretion of TGF-beta by both tumor cells and, in a paracrine fashion, stromal cells, is involved in the enhancement of tumor invasion and metastasis accompanied by immunosuppression. Herein, the authors review the clinical significance of FasL and TGF-beta expression patterns as features of immune privilege accompanying tumor progression in the tumor microenvironment. Potential strategies for identifying which molecules can serve as targets for effective antitumor therapy also are discussed.

Regulation of large-scale chromatin unfolding by Smad4

The tumor suppressor Smad4 plays a critical role in the transforming growth factor-beta (TGF-beta signaling pathway. Smad4 is an essential component of transcriptional complexes mediating the activation of Smad-dependent target genes. However, how Smad4 regulates various chromosomal events remains unknown. Here, we report that Smad4 induces large-scale chromatin unfolding by targeting Smad4 to an amplified, lac operator-containing chromosome region in mammalian cells. This unfolding activity maps to the subdomains within the transactivation domain of Smad4. Both the N-terminal missense and the C-terminal truncated tumor-derived mutations increased the chromatin unfolding activity of Smad4. These data identify a novel function of Smad4 and suggest that regulation of large-scale chromatin unfolding by Smad4 may be responsible for cancer development.

Status of the DPC4 tumor suppressor gene in sporadic colon adenocarcinoma of Croatian patients: identification of a novel somatic mutation

Loss of heterozygosity (LOH) of loci on chromosome 18q occurs in a majority of colorectal cancers. The DPC4 (Smad4) tumor suppressor gene, located at 18q21.1, may be a predisposing gene for Juvenile Polyposis Syndrome. To investigate alterations of the DPC4 gene in sporadic colon adenocarcinoma, a panel of 60 tumor specimens from Croatian patients was surveyed for evidence of LOH and also for mutations within the entire DPC4 coding region (exons 1-11). Using three pairs of specific primers for the three DPC4 microsatellite repetitive sequences, we investigated the frequency of LOH. The presence of single nucleotide change at restriction sites of specific codons in exons 2, 8, 10, and 11 (which belong to the conserved region of the gene) was examined by RFLP analysis. The investigation was extended to search for any other mutation within the entire coding region of the DPC4 gene by single strand conformation polymorphism (SSCP) analysis. Our results show a high frequency of heterozygosity in 58 of 60 (97%) colon adenocarcinoma samples. LOH at any one of the three flanking markers was observed in 26 (45%) of the 58 informative cases. The loss of one allele of the DPC4 gene was negatively correlated with tumor size; more frequent in smaller tumors (<5 cm) than in larger ones. A mutation was found in exon 11 in only one tumor sample (T18), and the mutation was verified by sequencing. Sequencing demonstrated a novel mutation-a deletion in exon 11 (134-153 del TAGACGAAGTACTTCATACC) of the DPC4 gene in the MH2 domain. These data suggest that inactivation of the DPC4 gene contributes to the genesis of colorectal carcinoma through allelic loss whereas mutation in the coding region of the DPC4 gene is infrequently detected in Croatian patients with A, B or C stages of colorectal cancers.