A stochastic carcinogenesis model incorporating multiple types of genomic instability fitted to colon cancer data

A generalization of the two-mutation stochastic carcinogenesis model of Moolgavkar, Venzon and Knudson and certain models constructed by Little [Little, M.P. (1995). Are two mutations sufficient to cause cancer? Some generalizations of the two-mutation model of carcinogenesis of Moolgavkar, Venzon, and Knudson, and of the multistage model of Armitage and Doll. Biometrics 51, 1278-1291] and Little and Wright [Little, M.P., Wright, E.G. (2003). A stochastic carcinogenesis model incorporating genomic instability fitted to colon cancer data. Math. Biosci. 183, 111-134] is developed; the model incorporates multiple types of progressive genomic instability and an arbitrary number of mutational stages. The model is fitted to US Caucasian colon cancer incidence data. On the basis of the comparison of fits to the population-based data, there is little evidence to support the hypothesis that the model with more than one type of genomic instability fits better than models with a single type of genomic instability. Given the good fit of the model to this large dataset, it is unlikely that further information on presence of genomic instability or of types of genomic instability can be extracted from age-incidence data by extensions of this model.     

Cancer models,genomic instability and somatic cellular Darwinian evolution

   

The biology of cancer is critically reviewed and evidence adduced that its development can be modelled as a somatic cellular Darwinian evolutionary process. The evidence for involvement of genomic instability (GI) is also reviewed. A variety of quasi-mechanistic models of carcinogenesis are reviewed, all based on this somatic Darwinian evolutionary hypothesis; in particular, the multi-stage model of Armitage and Doll (Br. J. Cancer 1954:8;1-12), the two-mutation model of Moolgavkar, Venzon, and Knudson (MVK) (Math. Biosci. 1979:47;55-77), the generalized MVK model of Little (Biometrics 1995:51;1278-1291) and various generalizations of these incorporating effects of GI (Little and Wright Math. Biosci. 2003:183;111-134; Little et al. J. Theoret. Biol. 2008:254;229-238).     

A stochastic carcinogenesis model incorporating genomic instability fitted to colon cancer data

A generalization of the two-mutation stochastic carcinogenesis model of Moolgavkar, Venzon and Knudson and certain models constructed by Little is developed; the model incorporates progressive genomic instability and an arbitrary number of mutational stages. This model is shown to have the property that, at least in the case when the parameters of the model are eventually constant, the excess relative and absolute cancer rates following changes in any of the parameters will eventually tend to zero. It is also shown that when the parameters governing the processes of cell division, death, or additional mutation (whether of the normal sort or that resulting in genomic destabilization) at the penultimate stage are subject to perturbations, there are relatively large fluctuations in the hazard function for the model, which start almost as soon as the parameters are changed. The model is fitted to US Caucasian colon cancer incidence data. A model with five stages and two levels of genomic destabilization fits the data well. Comparison with patterns of excess risk in the Japanese atomic bomb survivor colon cancer incidence data indicate that radiation might act on early mutation rates in the model; a major role for radiation in initiating genomic destabilization is less likely.     

Bayesian area–age–period–cohort model with carcinogenesis age effects in estimating cancer mortality

Objective: Area–age–period–cohort (AAPC) model has been widely used in studying the spatial and temporal pattern of disease incidence and mortality rates. However, lack of biological plausibility and ease of interpretability on temporal components especially for age effects are generally the weakness of AAPC models. We develop a Bayesian AAPC model where carcinogenesis age effect is incorporated to explain age effects from the underlying disease process. An autoregressive prior structure and an arbitrary linear constraint are used to solve the nonidentifiability issues. Methods: Two multistage carcinogenesis models are employed to derive the hazard functions to substitute the age effects in the AAPC models. The Iowa county-wide lung cancer mortality data are used for the model fitting and Deviance Information Criteria (DIC) is used for model comparison. Results: Our study shows that conventional AAPC model (DIC = 19,231.30), AAPC model with Armitage–Doll age effect (DIC = 19,233.00) and with two-stage clonal expansion (TSCE) age effect (DIC = 19,234.70) achieved the similar DIC values which indicated consistent model fitting among three models. The spatial pattern shows that the high spatial effects are clustered in the south of Iowa and also in largely populated areas. The lung cancer mortality rate is continuously declining by birth cohorts while increasing by the calendar period until 2000–2004. The age effects show an increasing pattern over time which can be easily explained by Armitage–Doll carcinogenesis model since we assume a log-linear relationship between age and hazard function. Conclusions: Our finding suggests that the proposed Bayesian AAPC model can be used to replace the conventional AAPC model without affecting model performance while providing a more biological sound approach from the underlining disease process.     

Asymptotic Relative Risk Results from a Simplified Armitage and Doll Model of Carcinogenesis

We examine basic asymptotic properties of relative risk for two families of generalized Erlang processes (where each one is based off of a simplified Armitage and Doll multistage model) in order to predict relative risk data from cancer. The main theorems that we are able to prove are all corroborated by large clinical studies involving relative risk for former smokers and transplant recipients. We then show that at least some of these theorems do not extend to other Armitage and Doll multistage models. We conclude with suggestions for lifelong increased cancer screening for both former smoker and transplant recipient subpopulations of individuals and possible future directions of research.     

Inactivation of both alleles of the DPC4/SMAD4 gene in advanced colorectal cancers: identification of seven novel somatic mutations in tumors from Japanese patients.

Loss of heterozygosity (LOH) of loci on chromosome 18q occurs in a majority of colorectal cancers. The DPC4/SMAD4 gene, lying in close proximity to the DCC gene at 18q21.1, was recently identified as a candidate tumor suppressor for the genesis of pancreatic cancer as well as a predisposing gene for Juvenile Polyposis Syndrome (JPS). The gene product functions as a cytoplasmic mediator in the signaling pathway of transforming growth factor beta (TGF-beta). To investigate the potential role of DPC4/SMAD4 gene in colorectal cancers, we examined 73 tumors of clinical stages II or III from Japanese patients, for LOH at 18q21 and also for subtle mutations anywhere within the coding region of DPC4/SMAD4. LOH was identified in 50 (78%) of the 64 tumors that were informative for polymorphic markers in the region. Somatic mutations were identified in seven of those tumors: two frameshift mutations, a 1-bp deletion (326 del T) in exon 8 and a 1-bp insertion (50-51 ins A) in exon 1; two nonsense mutations, Arg445Ter in exon 10 and Glu538Ter in exon 11; and three missense mutations, Asn129Lys in exon 2, Tyr95Asn in exon 2, and Asp355Glu in exon 8. Three of the seven mutations were observed in the mad homology 1 (MH1) domain encoded by exons 1 and 2. In all of the tumors carrying intragenic mutations of one allele, LOH analysis had shown that the other allele was missing. The results demonstrated that inactivation of both alleles of the DPC4/SMAD4 gene occurs in a substantial proportion of advanced colorectal cancers, and that the DPC4/SMAD4 gene probably exerts a tumor-suppressor effect for colorectal carcinogenesis that fulfills the criterion of the two-hit concept proposed by Knudson [A.G. Knudson, Hereditary cancer, oncogenes, and anti-oncogenes, Cancer Res. 45 (1985) 1437-1443.].     

Parameter Identifiability and Redundancy in a General Class of Stochastic Carcinogenesis Models

Background

Heidenreich et al. (Risk Anal 1997 17 391–399) considered parameter identifiability in the context of the two-mutation cancer model and demonstrated that combinations of all but two of the model parameters are identifiable. We consider the problem of identifiability in the recently developed carcinogenesis models of Little and Wright (Math Biosci 2003 183 111–134) and Little et al. (J Theoret Biol 2008 254 229–238). These models, which incorporate genomic instability, generalize a large number of other quasi-biological cancer models, in particular those of Armitage and Doll (Br J Cancer 1954 8 1–12), the two-mutation model (Moolgavkar et al. Math Biosci 1979 47 55–77), the generalized multistage model of Little (Biometrics 1995 51 1278–1291), and a recently developed cancer model of Nowak et al. (PNAS 2002 99 16226–16231).

Methodology/Principal Findings

We show that in the simpler model proposed by Little and Wright (Math Biosci 2003 183 111–134) the number of identifiable combinations of parameters is at most two less than the number of biological parameters, thereby generalizing previous results of Heidenreich et al. (Risk Anal 1997 17 391–399) for the two-mutation model. For the more general model of Little et al. (J Theoret Biol 2008 254 229–238) the number of identifiable combinations of parameters is at most less than the number of biological parameters, where is the number of destabilization types, thereby also generalizing all these results. Numerical evaluations suggest that these bounds are sharp. We also identify particular combinations of identifiable parameters.

Conclusions/Significance

We have shown that the previous results on parameter identifiability can be generalized to much larger classes of quasi-biological carcinogenesis model, and also identify particular combinations of identifiable parameters. These results are of theoretical interest, but also of practical significance to anyone attempting to estimate parameters for this large class of cancer models.     

Inactivation of both alleles of the DPC4/SMAD4 gene in advanced colorectal cancers: identification of seven novel somatic mutations in tumors from Japanese patients

Loss of heterozygosity (LOH) of loci on chromosome 18q occurs in a majority of colorectal cancers. The DPC4/SMAD4 gene, lying in close proximity to the DCC gene at 18q21.1, was recently identified as a candidate tumor suppressor for the genesis of pancreatic cancer as well as a predisposing gene for Juvenile Polyposis Syndrome (JPS). The gene product functions as a cytoplasmic mediator in the signaling pathway of transforming growth factor beta (TGF-β). To investigate the potential role of DPC4/SMAD4 gene in colorectal cancers, we examined 73 tumors of clinical stages II or III from Japanese patients, for LOH at 18q21 and also for subtle mutations anywhere within the coding region of DPC4/SMAD4. LOH was identified in 50 (78%) of the 64 tumors that were informative for polymorphic markers in the region. Somatic mutations were identified in seven of those tumors: two frameshift mutations, a 1-bp deletion (326 del T) in exon 8 and a 1-bp insertion (50–51 ins A) in exon 1; two nonsense mutations, Arg445Ter in exon 10 and Glu538Ter in exon 11; and three missense mutations, Asn129Lys in exon 2, Tyr95Asn in exon 2, and Asp355Glu in exon 8. Three of the seven mutations were observed in the mad homology 1 (MH1) domain encoded by exons 1 and 2. In all of the tumors carrying intragenic mutations of one allele, LOH analysis had shown that the other allele was missing. The results demonstrated that inactivation of both alleles of the DPC4/SMAD4 gene occurs in a substantial proportion of advanced colorectal cancers, and that the DPC4/SMAD4 gene probably exerts a tumor-suppressor effect for colorectal carcinogenesis that fulfills the criterion of the two-hit concept proposed by Knudson [A.G. Knudson, Hereditary cancer, oncogenes, and anti-oncogenes, Cancer Res. 45 (1985) 1437–1443.].     

Increased incidence of colon cancer among individuals younger than 50 years: A 17 years analysis from the cancer registry of the municipality of Milan,Italy

BackgroundColorectal cancer (CRC) overall incidence has been decreasing in the last decade. However, there is evidence of an increasing frequency of early-onset CRC in young individuals in several countries. The aim of this study is to evaluate the trends of CRC occurrence over 17 years in the municipality of Milan, Italy, focusing on early-onset CRC.Population and methodsThis retrospective study was performed using the Cancer Registry of the municipality of Milan, including all cases of CRC diagnosed 1999-2015. Incidence rates were stratified by age and anatomic subsite, and trends over time were measured using the estimated annual percentage change. Age-period-cohort modelling was used to disentangle the different effects.Results18,783 cases of CRC were included. CRC incidence rates among individuals aged 50–60 years declined annually by 3% both in colon and in rectal cancer. Conversely, in adults younger than 50 years, overall CRC occurrence increased annually by 0.7%, with a diverging trend for colon (+2.6%) and rectal (−5.3%) cancer. Among individuals aged 60 years and older, CRC incidence rates increased by 1.0% annually up to 2007, and decrease thereafter by 4% per year, both for colon and rectal cancer. Age-period-cohort models showed a reduction of CRC risk for the cohorts born up to 1979, followed by an increase in younger cohorts. In contrast, rectal cancer among women showed a systematic risk decrease for all birth cohorts.ConclusionsThe study highlights increasing incidence of colon cancer in younger subjects and a decrease in incidence rates for rectal cancer in females.     

Genomic Instability and Radiation Risk in Molecular Pathways to Colon Cancer

Colon cancer is caused by multiple genomic alterations which lead to genomic instability (GI). GI appears in molecular pathways of microsatellite instability (MSI) and chromosomal instability (CIN) with clinically observed case shares of about 15–20% and 80–85%. Radiation enhances the colon cancer risk by inducing GI, but little is known about different outcomes for MSI and CIN. Computer-based modelling can facilitate the understanding of the phenomena named above. Comprehensive biological models, which combine the two main molecular pathways to colon cancer, are fitted to incidence data of Japanese a-bomb survivors. The preferred model is selected according to statistical criteria and biological plausibility. Imprints of cell-based processes in the succession from adenoma to carcinoma are identified by the model from age dependences and secular trends of the incidence data. Model parameters show remarkable compliance with mutation rates and growth rates for adenoma, which has been reported over the last fifteen years. Model results suggest that CIN begins during fission of intestinal crypts. Chromosomal aberrations are generated at a markedly elevated rate which favors the accelerated growth of premalignant adenoma. Possibly driven by a trend of Westernization in the Japanese diet, incidence rates for the CIN pathway increased notably in subsequent birth cohorts, whereas rates pertaining to MSI remained constant. An imbalance between number of CIN and MSI cases began to emerge in the 1980s, whereas in previous decades the number of cases was almost equal. The CIN pathway exhibits a strong radio-sensitivity, probably more intensive in men. Among young birth cohorts of both sexes the excess absolute radiation risk related to CIN is larger by an order of magnitude compared to the MSI-related risk. Observance of pathway-specific risks improves the determination of the probability of causation for radiation-induced colon cancer in individual patients, if their exposure histories are known.     

肿瘤干细胞与卵巢癌研究进展

近年来,肿瘤干细胞学说作为肿瘤发生发展的重要原因获得越来越多的认可。肿瘤干细胞是指肿瘤中存在的含量极少、具有无限增殖潜能的干细胞样肿瘤细胞,它们能自我更新、分化、迁徙,是导致肿瘤发生、发展、转移和耐药的重要原因。卵巢癌也可能是卵巢癌干细胞所致的疾病。卵巢癌干细胞的分离鉴定正处于起始阶段,针对卵巢癌干细胞的靶向治疗可能在卵巢癌治疗中具有重要作用,为临床彻底治愈卵巢癌带来希望。     

Modeling age-specific incidence of colon cancer via niche competition

Cancer development is a multistep process often starting with a single cell in which a number of epigenetic and genetic alterations have accumulated thus transforming it into a tumor cell. The progeny of such a single benign tumor cell expands in the tissue and can at some point progress to malignant tumor cells until a detectable tumor is formed. The dynamics from the early phase of a single cell to a detectable tumor with billions of tumor cells are complex and still not fully resolved, not even for the well-known prototype of multistage carcinogenesis, the adenoma-adenocarcinoma sequence of colorectal cancer. Mathematical models of such carcinogenesis are frequently tested and calibrated based on reported age-specific incidence rates of cancer, but they usually require calibration of four or more parameters due to the wide range of processes these models aim to reflect. We present a cell-based model, which focuses on the competition between wild-type and tumor cells in colonic crypts, with which we are able reproduce epidemiological incidence rates of colon cancer. Additionally, the fraction of cancerous tumors with precancerous lesions predicted by the model agree with clinical estimates. The correspondence between model and reported data suggests that the fate of tumor development is majorly determined by the early phase of tumor growth and progression long before a tumor becomes detectable. Due to the focus on the early phase of tumor development, the model has only a single fit parameter, the time scale set by an effective replacement rate of stem cells in the crypt. We find this effective rate to be considerable smaller than the actual replacement rate, which implies that the time scale is limited by the processes succeeding clonal conversion of crypts.     

Protein kinase C betaII and TGFbetaRII in omega-3 fatty acid-mediated inhibition of colon carcinogenesis

Increasing evidence demonstrates that protein kinase C betaII (PKCbetaII) promotes colon carcinogenesis. We previously reported that colonic PKCbetaII is induced during colon carcinogenesis in rodents and humans, and that elevated expression of PKCbetaII in the colon of transgenic mice enhances colon carcinogenesis. Here, we demonstrate that PKCbetaII represses transforming growth factor beta receptor type II (TGFbetaRII) expression and reduces sensitivity to TGF-beta-mediated growth inhibition in intestinal epithelial cells. Transgenic PKCbetaII mice exhibit hyperproliferation, enhanced colon carcinogenesis, and marked repression of TGFbetaRII expression. Chemopreventive dietary omega-3 fatty acids inhibit colonic PKCbetaII activity in vivo and block PKCbetaII-mediated hyperproliferation, enhanced carcinogenesis, and repression of TGFbetaRII expression in the colonic epithelium of transgenic PKCbetaII mice. These data indicate that dietary omega-3 fatty acids prevent colon cancer, at least in part, through inhibition of colonic PKCbetaII signaling and restoration of TGF-beta responsiveness.     

A Novel Clinically Relevant Animal Model for Studying Galectin-3 and Its Ligands During Colon Carcinogenesis

Galectin-3 (Gal-3) is a multifunctional protein that plays different roles in cancer biology. To better understand the role of Gal-3 and its ligands during colon carcinogenesis, we studied its expression in tumors induced in rats treated with 1,2-dimethylhydrazine (DMH) and in human tissues. Normal colon from untreated rats showed no staining using two specific monoclonal antibodies. In contrast, morphologically normal colon from DMH-treated rats and dysplastic aberrant crypt foci were strongly stained, indicating that increased Gal-3 expression is an early event during the neoplastic transformation in colon cells. Gal-3 was weakly expressed in adenocarcinomas. Overall, the Gal-3 expression pattern observed in the DMH rat model closely resembles that displayed by human colon stained with the same antibodies. We also found that Gal-3 phosphorylation diminishes in serines while increasing in tyrosines during rat colon carcinogenesis. Finally, we showed that Gal-3–ligands expression is strikingly similar in rat and human malignant colon and in non-malignant tissues. In conclusion, the DMH-induced rat colon cancer model displays expression patterns of Gal-3 and its ligands very similar to those observed in human samples. This animal model should contribute to clarifying the role of Gal-3 in colon carcinogenesis and also to finding effective preventive cancer agents based on Gal-3 targeting. (J Histochem Cytochem 58:553–565, 2010)     

中国人结肠癌nm23H1基因遗传不稳定性的研究

Techniques such as DNA extraction from paraffin-embedded tissues, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), ordinary silver stain, Envision immunohistochemistry and Leica-Qwin computer imaging techniques were used to study microsatellite instability (MSI) and loss of heterozygosity (LOH) of locus D17S396 at the 17th chromosome of Chinese patients and their influence on the expression of gene nm23H1, and to clarify the relationship between the genetic instability of gene nm23H1 and the development of colon cancer, which may provide experimental basis for clinical treatment. In our experiments, the frequency of MSI, LOH and nm23H1 protein reacted positive of 30 cases of colon cancer were 26.67%, 20.00% and 53.33% respectively. In tumor node metastasis (TNM) staging, the positive frequency of MSI (43.75%) and nm23H1 protein (81.25%) in stage I + II were more than those (MSI 7.14%, p < 0.05 and nm23H1 21.43%, p < 0.01) in stage III + IV, while the frequency of LOH (35.71%), which had a rising trend along with the Duke's staging increasing, was higher than that of LOH (6.25%, p < 0.05) in stage I + II. The positive frequency of nm23H1 protein in the group of tubular adenocarcinoma (60.00%) was distinctively higher than that in the group of mucoid adenocarcinoma (20.00%, p < 0.01), showing a rising trend along with the increase of the differentiation degree of tubular adenocarcinoma. Furthermore, the positive frequency of nm23H1 protein in MSI positive group was also higher than MSI negative group (p < 0.05). And there was no difference in nm23H1 protein expression analyzed by computer imaging techniques. The results of experiments indicated that both MSI and LOH controlled the development of sporadic colon cancer independently in different paths. LOH occurred mostly in the late period of sporadic colon cancer and endowed with it a high aggressive and poor prognosis. In contrast, MSI was an early period molecule marker of sporadic colon cancer. Increasing the amount of nm23H1 protein expression could effectively restrain colon cancer metastasis and improved prognosis of sporadic colon cancer patients.     

Down-regulation of the tumor suppressor gene C-terminal Src kinase: an early event during premalignant colonic epithelial hyperproliferation

Hyperproliferation of the premalignant epithelium is critical for colonic carcinogenesis; however the mechanisms remain largely unexplored. We report herein that prior to occurrence of neoplastic lesions in the azoxymethane-rat model of colon carcinogenesis; the tumor suppressor gene C-terminal Src kinase (Csk) was down-regulated with a concomitant increase in Src activity. Furthermore, pharmacological or genetic (RNA interference) inhibition of Csk resulted in increased proliferation in colon cancer cell lines through the mitogen-activated protein kinase dependent pathway. Thus, we demonstrate, for the first time, that Csk suppression is an important early event in colorectal cancer pathogenesis.     

中国人胃癌染色体17q21区域基因遗传不稳定性研究

To investigate microsatellite instability (MSI) and loss of heterozygosity (LOH) of locus D17S396, D17S579 and D17S855, and their effect on the expression of nm23H1 and BRCA1 of gastric cancer, which would provide experimental basis for clinical treatment and prognosis analysis of gastric cancer. DNA was extracted from paraffin-embedded materials. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) was used to analyze MSI and LOH. Expression of nm23H, and BRCA1 was detected by Envision immuno-histochemistry and Leica-Qwin computer imaging techniques. In the forty cases of gastric cancer, the frequency of MSI, LOH and nm23H1 protein were 20.00%, 17.50% and 55.00% respectively at locus D17S396, while at locus D17S579, the frequency of MSI, LOH and BRCA1 protein were 22.50%, 15.00% and 37.50% respectively; at locus D17S855, the frequency of MSI, LOH and BRCA1 of thirty-seven cases were 18.92%, 18.92%, 37.84% respectively. In tumor node metastasis (TNM) staging, at locus D17S396, D17S579 and D17S855, MSI in stages I + II appeared more frequently than that in stages III + IV, while LOH appeared the contrary tendency. In the group of metastasis of gastric cancer, MSI had a less frequency (5.00%) than that with no metastasis (35.00%, P < 0.05) at locus D17S396, but LOH appeared more frequently (30.00%) than that with no metastasis (5.00%, P < 0.05). At locus D17S579, MSI had an increasing tendency with the degree of tumor differentiation (50.00% in high differentiation cases, 20.00% in middle differentiation cases, and 0% in low differentiation cases, P < 0.05). The frequency of nm23H1 and BRCA1 protein in stages TNM I + II was higher than that in stages TNM III + IV; and that in higher differentiation cases was higher than in poor differentiation cases. The frequency of nm23H1 protein in the group of metastasis (30.00%) was less than that with no metastasis significantly (80.00%, P<0.01). The frequency of nm23H1 protein in the group positive to MSI (87.50%) was higher than that in the group negative to MSI (46.88%, P < 0.05). However, nm23H1 protein in group positive to LOH (14.29%) was lower than that in the group negative to LOH (63.64%, P < 0.05). The frequency of BRCA1 protein in the group positive to MSI (66.67%) was more than that in the group negative to MSI (29.03%, P < 0.05). The results of experiments indicate that MSI and LOH may separately control the development of sporadic colon cancer with different pathways. MSI may be an early period molecule marker for sporadic colon cancer, enhanced expression of nm23H1 protein can effectively inhibit colon cancer metastasis and improve prognosis of sporadic colon cancer patients. By comparison, LOH mostly arises in the late period of sporadic colon cancer and endows a high aggressive and poor prognostic phenotype. nm23H1 protein could effectively restrain gastric cancer metastasis and development; and BRCA1 protein could restain tumor from becoming lower differentiation.