MicroRNAs as potential liquid biopsy biomarkers in colorectal cancer: A systematic review

Emerging evidence has demonstrated the feasibility of circulating miRNAs as robust non-invasive biomarkers for the diagnosis in colorectal cancer. The use of circulating miRNAs for the early detection of colorectal cancer (CRC) is of particular interest as it can offer a potential complementary approach to screening colonoscopy. However, the development of circulating miRNAs as "liquid biopsy" biomarkers for development into clinical screening tests has been hampered by several issues. In this article, we summarize the status of this field for the clinical utilization of miRNA biomarkers as liquid biopsies in colorectal cancer (CRC) and discuss their applications as screening tests for patients with colorectal adenoma (CRA) and CRC. Herein, we undertook a systematic search for citations in PubMed and the Cochrane Database from January 1, 2002 through December 31, 2017 as electronic sources for this study. All published studies were screened with no restriction on language, date, or country. We used database-specific combinations of the following index terms and text words, including: microRNA, colorectal cancer, serum, plasma, and exosomes. Based upon these searches, we summarize the progress and salient features of the current state of knowledge of miRNA diagnostic biomarkers in CRC, and focuses on the articles that attempt to optimize ideal methodologies to further advance their as liquid biopsies for clinical use. We conclude that the field of noncoding RNAs, particularly for the clinical use of miRNAs as liquid biopsy assays is maturing rapidly, and it is highly promising that these genomic signatures will likely be developed into clinically-viable tests for the early detection and clinical management of patients with colorectal cancer in the not so distant future.

Effect of aspirin on tumour cell colony formation and evolution

Aspirin is known to reduce the risk of colorectal cancer (CRC) incidence, but the underlying mechanisms are not fully understood. In a previous study, we quantified the in vitro growth kinetics of different CRC tumour cell lines treated with varying doses of aspirin, measuring the rate of cell division and cell death. Here, we use these measured parameters to calculate the chances of successful clonal expansion and to determine the evolutionary potential of the tumour cell lines in the presence and absence of aspirin. The calculations indicate that aspirin increases the probability that a single tumour cell fails to clonally expand. Further, calculations suggest that aspirin increases the evolutionary potential of an expanding tumour cell colony. An aspirin-treated tumour cell population is predicted to result in the accumulation of more mutations (and is thus more virulent and more difficult to treat) than a cell population of the same size that grew without aspirin. This indicates a potential trade-off between delaying the onset of cancer and increasing its evolutionary potential through chemoprevention. Further work needs to investigate to what extent these findings apply to in vivo settings, and to what degree they contribute to the epidemiologically documented aspirin-mediated protection.

Recent progress in Lynch syndrome and other familial colorectal cancer syndromes

The current understanding of familial colorectal cancer was limited to descriptions of affected pedigrees until the early 1990s. A series of landscape-altering discoveries revealed that there were distinct forms of familial cancer, and most were related to genes previously not known to be involved in human disease. This review largely focuses on advances in our understanding of Lynch syndrome because of the unique relationship of this disease to defective DNA mismatch repair and the clinical implications this has for diagnostics, prevention, and therapy. Recent advances have occurred in our understanding of the epidemiology of this disease, and the advent of broad genetic panels has altered the approach to germline and somatic diagnoses for all of the familial colorectal cancer syndromes. Important advances have been made toward a more complete mechanistic understanding of the pathogenesis of neoplasia in the setting of Lynch syndrome, and these advances have important implications for prevention. Finally, paradigm-shifting approaches to treatment of Lynch-syndrome and related tumors have occurred through the development of immune checkpoint therapies for hypermutated cancers. CA Cancer J Clin 2018;68:217-231. © 2018 American Cancer Society.

TFAP2E Methylation and Expression Status Does Not Predict Response to 5-FU-based Chemotherapy in Colorectal Cancer

Purpose: A recent study reported that 5-fluorouracil (5-FU)-based chemotherapy is less effective in treating patients with advanced colorectal cancer demonstrating hypermethylation of the TFAP2E gene. The aim of our study was to confirm and validate these findings in large, uniformly treated, well-characterized patient cohorts.Experimental Design: Two cohorts of 783 patients with colorectal cancer: 532 from a population-based, multicenter cohort (EPICOLON I) and 251 patients from a clinic-based trial were used to study the effectiveness of TFAP2E methylation and expression as a predictor of response of colorectal cancer patients to 5-FU-based chemotherapy. DNA methylation status of the TFAP2E gene in patients with colorectal cancer was assessed by quantitative bisulfite pyrosequencing analysis. IHC analysis of the TFAP2E protein expression was also performed.Results: Correlation between TFAP2E methylation status and IHC staining was performed in 607 colorectal cancer samples. Among 357 hypermethylated tumors, only 141 (39.6%) exhibited loss of protein expression. Survival was not affected by TFAP2E hypermethylation in stage IV patients [HR, 1.21; 95% confidence interval (CI), 0.79-1.87; log-rank P = 0.6]. In stage II-III cases, disease-free survival was not influenced by TFAP2E hypermethylation status in 5-FU-treated (HR, 0.91; 95% CI, 0.52-1.59; log-rank P = 0.9) as well as in nontreated patients (HR, 0.88; 95% CI, 0.5-1.54; log-rank P = 0.7).Conclusions:TFAP2E hypermethylation does not correlate with loss of its protein expression. Our large, systematic, and comprehensive study indicates that TFAP2E methylation and expression may not play a major role in predicting response to 5-FU-based chemotherapy in patients with colorectal cancer. Clin Cancer Res; 24(12); 2820-7. ©2018 AACR.

Accuracy of four mononucleotide-repeat markers for the identification of DNA mismatch-repair deficiency in solid tumors

Background

To screen tumors with microsatellite instability (MSI) arising due to DNA mismatch repair deficiency (dMMR), a panel of five quasi-monomorphic mononucleotide-repeat markers amplified in a multiplex PCR (Pentaplex) are commonly used. In spite of its several strengths, the pentaplex assay is not robust at detecting the loss of MSH6-deficiency (dMSH6). In order to overcome this challenge, we designed this study to develop and optimize a panel of four quasi-monomorphic mononucleotide-repeat markers (Tetraplex) for identifying solid tumors with dMMR, especially dMSH6.

Methods

To improve the sensitivity for tumors with dMMR, we established a quasi-monomorphic variant range (QMVR) of 3–4 bp for the four Tetraplex markers. Thereafter, to confirm the accuracy of this assay, we examined 317 colorectal cancer (CRC) specimens, comprising of 105 dMMR [45 MutL homolog (MLH)1-deficient, 45 MutS protein homolog (MSH)2-deficient, and 15 MSH6-deficient tumors] and 212 MMR-proficient (pMMR) tumors as a test set. In addition, we analyzed a cohort of 138 endometrial cancers (EC) by immunohistochemistry to determine MMR protein expression and validation of our new MSI assay.

Results

Using the criteria of ≥ 1 unstable markers as MSI-positive tumor, our assay resulted in a sensitivity of 97.1% [95% confidence interval (CI) = 91.9–99.0%] for dMMR, and a specificity of 95.3% (95% CI = 91.5–97.4%) for pMMR CRC specimens. Among the 138 EC specimens, 41 were dMMR according to immunohistochemistry. Herein, our Tetraplex assay detected dMMR tumors with a sensitivity of 92.7% (95% CI = 80.6–97.5%) and a specificity of 97.9% (95% CI = 92.8–99.4%) for pMMR tumors. With respect to tumors with dMSH6, in the CRC-validation set, Tetraplex detected dMSH6 tumors with a sensitivity of 86.7% (13 of 15 dMSH6 CRCs), which was subsequently validated in the EC test set as well (sensitivity, 75.0%; 6 of 8 dMSH6 ECs).

Conclusions

Our newly optimized Tetraplex system will help offer a robust and highly sensitive assay for the identification of dMMR in solid tumors.

Electronic supplementary material

The online version of this article (10.1186/s12967-017-1376-4) contains supplementary material, which is available to authorized users.

A Panel of Methylated MicroRNA Biomarkers for Identifying High-Risk Patients With Ulcerative Colitis-Associated Colorectal Cancer

BACKGROUND & AIMS

Methylation of specific microRNAs (miRNAs) often occurs in an age-dependent manner, as a field defect in some instances, and may be an early event in colitis-associated carcinogenesis. We aimed to determine whether specific mRNA signature patterns (MIR1, MIR9, MIR124, MIR137, MIR34B/C) could be used to identify patients with ulcerative colitis (UC) who are at increased risk for colorectal neoplasia.

METHODS

We obtained 387 colorectal tissue specimens collected from 238 patients with UC (152 without neoplasia, 17 with dysplasia, and 69 with UC-associated colorectal cancer [UC-CRC]), from 2 independent cohorts in Japan between 2005 and 2015. We quantified methylation of miRNAs by bisulfite pyrosequencing analysis. We analyzed clinical data to determine whether miRNA methylation patterns were associated with age, location, or segment of the colorectum (cecum, transverse colon, and rectum). Differences in tissue miRNA methylation and expression levels were compared among samples and associated with cancer risk using the Wilcoxon, Mann-Whitney, and Kruskal-Wallis tests as appropriate. We performed a validation study of samples from 90 patients without UC and 61 patients with UC-associated dysplasia or cancer to confirm the association between specific methylation patterns of miRNAs in non-tumor rectal mucosa from patients with UC at risk of UC-CRC.

RESULTS

Among patients with UC without neoplasia, rectal tissues had significantly higher levels of methylation levels of MIR1, MIR9, MIR124, and MIR137 than in proximal mucosa; levels of methylation were associated with age and duration of UC in rectal mucosa. Methylation of all miRNAs was significantly higher in samples from patients with dysplasia or CRC compared with samples from patients without neoplasia. Receiver operating characteristic analysis revealed that methylation levels of miRNAs in rectal mucosa accurately differentiated patients with CRC from those without. Methylation of MIR137 in rectal mucosa was an independent risk factor for UC-CRC. Methylation patterns of a set of miRNAs (panel) could discriminate discriminate UC patients with or without dysplasia or CRC in the evaluation cohort (area under the curve, 0.81) and the validation cohort (area under the curve, 0.78).

CONCLUSIONS

In evaluation and validation cohorts, we found specific miRNAs to be methylated in rectal mucosal samples from patients with UC with dysplasia or CRC compared with patients without neoplasms. This pattern also associated with patient age and might be used to identify patients with UC at greatest risk for developing UC-CRC. Our findings provide evidence for a field defect in rectal mucosa from patients with UC-CRC.

Colorectal Cancer Screening: Recommendations for Physicians and Patients From the U.S. Multi-Society Task Force on Colorectal Cancer

This document updates the colorectal cancer (CRC) screening recommendations of the U.S. Multi-Society Task Force of Colorectal Cancer (MSTF), which represents the American College of Gastroenterology, the American Gastroenterological Association, and The American Society for Gastrointestinal Endoscopy. CRC screening tests are ranked in 3 tiers based on performance features, costs, and practical considerations. The first-tier tests are colonoscopy every 10 years and annual fecal immunochemical test (FIT). Colonoscopy and FIT are recommended as the cornerstones of screening regardless of how screening is offered. Thus, in a sequential approach based on colonoscopy offered first, FIT should be offered to patients who decline colonoscopy. Colonoscopy and FIT are recommended as tests of choice when multiple options are presented as alternatives. A risk-stratified approach is also appropriate, with FIT screening in populations with an estimated low prevalence of advanced neoplasia and colonoscopy screening in high prevalence populations. The second-tier tests include CT colonography every 5 years, the FIT-fecal DNA test every 3 years, and flexible sigmoidoscopy every 5 to 10 years. These tests are appropriate screening tests, but each has disadvantages relative to the tier 1 tests. Because of limited evidence and current obstacles to use, capsule colonoscopy every 5 years is a third-tier test. We suggest that the Septin9 serum assay (Epigenomics, Seattle, Wash) not be used for screening. Screening should begin at age 50 years in average-risk persons, except in African Americans in whom limited evidence supports screening at 45 years. CRC incidence is rising in persons under age 50, and thorough diagnostic evaluation of young persons with suspected colorectal bleeding is recommended. Discontinuation of screening should be considered when persons up to date with screening, who have prior negative screening (particularly colonoscopy), reach age 75 or have <10 years of life expectancy. Persons without prior screening should be considered for screening up to age 85, depending on age and comorbidities. Persons with a family history of CRC or a documented advanced adenoma in a first-degree relative age <60 years or 2 first-degree relatives with these findings at any age are recommended to undergo screening by colonoscopy every 5 years, beginning 10 years before the age at diagnosis of the youngest affected relative or age 40, whichever is earlier. Persons with a single first-degree relative diagnosed at ≥60 years with CRC or an advanced adenoma can be offered average-risk screening options beginning at age 40 years.

Colorectal Cancer Screening: Recommendations for Physicians and Patients from the U.S. Multi-Society Task Force on Colorectal Cancer

This document updates the colorectal cancer (CRC) screening recommendations of the U.S. Multi-Society Task Force of Colorectal Cancer (MSTF), which represents the American College of Gastroenterology, the American Gastroenterological Association, and The American Society for Gastrointestinal Endoscopy. CRC screening tests are ranked in 3 tiers based on performance features, costs, and practical considerations. The first-tier tests are colonoscopy every 10 years and annual fecal immunochemical test (FIT). Colonoscopy and FIT are recommended as the cornerstones of screening regardless of how screening is offered. Thus, in a sequential approach based on colonoscopy offered first, FIT should be offered to patients who decline colonoscopy. Colonoscopy and FIT are recommended as tests of choice when multiple options are presented as alternatives. A risk-stratified approach is also appropriate, with FIT screening in populations with an estimated low prevalence of advanced neoplasia and colonoscopy screening in high prevalence populations. The second-tier tests include CT colonography every 5 years, the FIT-fecal DNA test every 3 years, and flexible sigmoidoscopy every 5 to 10 years. These tests are appropriate screening tests, but each has disadvantages relative to the tier 1 tests. Because of limited evidence and current obstacles to use, capsule colonoscopy every 5 years is a third-tier test. We suggest that the Septin9 serum assay (Epigenomics, Seattle, Wash) not be used for screening. Screening should begin at age 50 years in average-risk persons, except in African Americans in whom limited evidence supports screening at 45 years. CRC incidence is rising in persons under age 50, and thorough diagnostic evaluation of young persons with suspected colorectal bleeding is recommended. Discontinuation of screening should be considered when persons up to date with screening, who have prior negative screening (particularly colonoscopy), reach age 75 or have <10 years of life expectancy. Persons without prior screening should be considered for screening up to age 85, depending on age and comorbidities. Persons with a family history of CRC or a documented advanced adenoma in a first-degree relative age <60 years or 2 first-degree relatives with these findings at any age are recommended to undergo screening by colonoscopy every 5 years, beginning 10 years before the age at diagnosis of the youngest affected relative or age 40, whichever is earlier. Persons with a single first-degree relative diagnosed at ≥60 years with CRC or an advanced adenoma can be offered average-risk screening options beginning at age 40 years.

Recommendations on Surveillance and Management of Biallelic Mismatch Repair Deficiency (BMMRD) Syndrome: A Consensus Statement by the US Multi-Society Task Force on Colorectal Cancer

The US Multi-Society Task Force on Colorectal Cancer, with invited experts, developed a consensus statement and recommendations to assist health care providers with appropriate management of patients with biallelic mismatch repair deficiency (BMMRD) syndrome, also called constitutional mismatch repair deficiency syndrome. This position paper outlines what is known about BMMRD, the unique genetic and clinical aspects of the disease, and reviews the current management approaches to this disorder. This article represents a starting point from which diagnostic and management decisions can undergo rigorous testing for efficacy. There is a lack of strong evidence and a requirement for further research. Nevertheless, providers need direction on how to recognize and care for BMMRD patients today. In addition to identifying areas of research, this article provides guidance for surveillance and management. The major challenge is that BMMRD is rare, limiting the ability to accumulate unbiased data and develop controlled prospective trials. The formation of effective international consortia that collaborate and share data is proposed to accelerate our understanding of this disease.

Recommendations on Surveillance and Management of Biallelic Mismatch Repair Deficiency (BMMRD) Syndrome: A Consensus Statement by the US Multi-Society Task Force on Colorectal Cancer

The US Multi-Society Task Force on Colorectal Cancer, with invited experts, developed a consensus statement and recommendations to assist health care providers with appropriate management of patients with biallelic mismatch repair deficiency (BMMRD) syndrome, also called constitutional mismatch repair deficiency syndrome. This position paper outlines what is known about BMMRD, the unique genetic and clinical aspects of the disease, and reviews the current management approaches to this disorder. This article represents a starting point from which diagnostic and management decisions can undergo rigorous testing for efficacy. There is a lack of strong evidence and a requirement for further research. Nevertheless, providers need direction on how to recognize and care for BMMRD patients today. In addition to identifying areas of research, this article provides guidance for surveillance and management. The major challenge is that BMMRD is rare, limiting the ability to accumulate unbiased data and develop controlled prospective trials. The formation of effective international consortia that collaborate and share data is proposed to accelerate our understanding of this disease.

Morphological characterization of colorectal cancers in The Cancer Genome Atlas reveals distinct morphology-molecular associations: clinical and biological implications

The Cancer Genome Atlas data on colorectal carcinoma have provided a comprehensive view of the tumor's genomic alterations and their tumorigenic roles. Tumor morphology, however, has not been fully integrated into the analysis. The aim of this study was to explore relevant associations between tumor morphology and the newly characterized genomic alterations in colorectal carcinoma. Two hundred and seven colorectal carcinomas that had undergone whole-exome sequencing as part of The Cancer Genome Atlas project and had adequate virtual images in the cBioPortal for Cancer Genomics constituted our study population. Upon analysis, a tight association between 'microsatellite instability-high histology' and microsatellite instability-high (P<0.001) was readily detected and helped validate our image-based histology evaluation. Further, we showed, (1) among all histologies, the not otherwise specified type had the lowest overall mutation count (P<0.001 for entire cohort, P<0.03 for the microsatellite-instable group), and among the microsatellite-instable tumors, this type also correlated with fewer frameshift mutations in coding mononucleotide repeats of a defined set of relevant genes (P<0.01); (2) cytosine phosphate guanine island methylator phenotype-high colorectal cancers with or without microsatellite instability tended to have different histological patterns: the former more often mucinous and the latter more often not otherwise specified; (3) mucinous histology was associated with more frequent alterations in BRAF, PIK3CA, and the transforming growth factor-β pathway when compared with non-mucinous histologies (P<0.001, P=0.01, and P<0.001, respectively); and (4) few colorectal cancers (<9%) exhibited upregulation of immune-inhibitory genes including major immune checkpoints; these tumors were primarily microsatellite-instable (up to 43%, vs <3% in microsatellite-stable group) and had distinctly non-mucinous histologies with a solid growth. These morphology-molecular associations are interesting and propose important clinical implications. The morphological patterns associated with alterations of immune checkpoint genes bear the potential to guide patient selection for clinical trials that target immune checkpoints in colorectal cancer, and provide directions for future studies.

Recommendations on Fecal Immunochemical Testing to Screen for Colorectal Neoplasia: A Consensus Statement by the US Multi-Society Task Force on Colorectal Cancer

The use of the fecal occult blood test (FOBT) for colorectal cancer (CRC) screening is supported by randomized trials demonstrating effectiveness in cancer prevention and widely recommended by guidelines for this purpose. The fecal immunochemical test (FIT), as a direct measure of human hemoglobin in stool has a number of advantages relative to conventional FOBT and is increasingly used relative to that test. This review summarizes current evidence for FIT in colorectal neoplasia detection and the comparative effectiveness of FIT relative to other commonly used CRC screening modalities. Based on evidence, guidance statements on FIT application were developed and quality metrics for program implementation proposed.

Circulating microRNA-203 predicts prognosis and metastasis in human colorectal cancer

BACKGROUND AND AIMS

Distant metastasis is a major cause of deaths in patients with colorectal cancer (CRC), which is partly due to lack of robust metastasis-predictive biomarkers. In spite of the important function of microRNA (miR)-203 in cancer metastasis, its clinical significance in CRC metastasis remains unknown. Here, we evaluated the potential role of serum miR-203 as a non-invasive biomarker for CRC metastasis.

METHODS

MiR-203 expression was quantified by quantitative reverse-transcription PCR in 58 pairs of primary CRC (pCRC) and corresponding matched liver metastasis (LM), as well as 186 serum and 154 matched tissue specimens from patients with CRC in cohort 1. Next, we performed validation of miR-203 levels in serum from 144 patients with CRC in an independent cohort (cohort 2). Mouse models of CRC-associated metastases were established to identify the source of circulating miR-203. Expression patterns of miR-203 in tissues were determined by in situ hybridisation.

RESULTS

MiR-203 expression was significantly upregulated in LM compared with matched pCRC tissues. Serum miR-203 levels were significantly upregulated in a stage-dependent manner, and high miR-203 expression was associated with poor survival in patients with CRC in both patient cohorts. Increased miR-203 levels in serum indicated high risk for poor prognosis (HR=2.1), as well as metastasis to lymph nodes (OR=2.5), liver (OR=6.2), peritoneum (OR=7.2) and distant organs (OR=4.4). Serum miR-203 levels were significantly higher in animals with liver or systemic metastasis compared with controls.

CONCLUSIONS

High levels of serum miR-203 associate with poor survival and metastasis, suggesting it to be a promising non-invasive prognostic and metastasis-predictive biomarker in patients with CRC.

Historical Perspective on Familial Gastric Cancer

Gastric cancer is a common disease worldwide, typically associated with acquired chronic inflammation in the stomach, related in most instances to infection by Helicobacter pylori. A small percentage of cases occurs in familial clusters, and some of these can be linked to specific germline mutations. This article reviews the historical background to the current understanding of familial gastric cancer, focuses on the entity of hereditary diffuse gastric cancer, and also reviews the risks for gastric cancer related to a number of other familial genetic diseases.

Aspirin-Induced Chemoprevention and Response Kinetics Are Enhanced by PIK3CA Mutations in Colorectal Cancer Cells

This study was designed to determine how aspirin influences the growth kinetics and characteristics of cultured colorectal cancer cells that harbor a variety of different mutational backgrounds, including PIK3CA- and KRAS-activating mutations, and the presence or absence of microsatellite instability. Colorectal cancer cell lines (HCT116, HCT116 + Chr3/5, RKO, SW480, HCT15, CACO2, HT29, and SW48) were treated with pharmacologically relevant doses of aspirin (0.5-10 mmol/L) and evaluated for proliferation and cell-cycle distribution. These parameters were fitted to a mathematical model to quantify the effects and understand the mechanism(s) by which aspirin modifies growth in colorectal cancer cells. We also evaluated the effects of aspirin on key G₀-G₁ cell-cycle genes that are regulated by the PI3K-Akt pathway. Aspirin decelerated growth rates and disrupted cell-cycle dynamics more profoundly in faster growing colorectal cancer cell lines, which tended to be PIK3CA mutants. Additionally, microarray analysis of 151 colorectal cancer cell lines identified important cell-cycle regulatory genes that are downstream targets of PIK3 and were also dysregulated by aspirin treatment (PCNA and RB1). Our study demonstrated what clinical trials have only speculated, that PIK3CA-mutant colorectal cancers are more sensitive to aspirin. Aspirin inhibited cell growth in all colorectal cancer cell lines regardless of mutational background, but the effects were exacerbated in cells with PIK3CA mutations. Mathematical modeling combined with bench science revealed that cells with PIK3CA-mutations experience significant G₀-G₁ arrest and explains why patients with PIK3CA mutant colorectal cancers may benefit from aspirin use after diagnosis. Cancer Prev Res; 10(3); 208-18. ©2017 AACR.

Abstract IA02: The discovery of the hereditary colorectal cancer genes: A historical perspective

When I was first introduced to the concept of carcinogenesis as a medical student in 1969, the problem was conceptually a “black box”. Certain stimuli were carcinogenic, something happened to a cell, and cancer resulted. It had been noted in the beginning of the 20th Century that cancer cells had abnormal chromosomes (Boveri); it had been noted that chicken sarcomas could be transmitted by a “filterable agent” (Rous sarcoma virus); a variety of compounds could cause cancers on the skin of mice (chemical carcinogenesis), as well other physical agents (UV light, Xrays). There were other empirical observations, but there were no unifying concepts of what was inside the black box of any cancer, let alone the hereditary forms.

The mechanisms of inheritance were known to be related to the nucleus, but it was not until 1953 that the structure of DNA was deduced, and actually a few years later that the number of human chromosomes was accurately determined to be 46. Concepts of inheritance were entirely descriptive. Progress was excruciatingly slow. It had been a century since the initial appreciation of dominant and recessive inheritance. However, only a few diseases with very distinctive phenotypes were clearly identified as familial, and only a few of these had any biochemical explanation. There was no obvious place to begin the search for the genetic basis of familial diseases. Worse, for the more common diseases such as cancer, diabetes and hypertension, it was thought that environmental influences were much more important than genetic ones.

The discovery process accelerated through technical advances that permitted deeper dives into the genetic processes underlying these diseases. Chromosomal banding was only useful when there were grossly detectable defects in a chromosome. DNA sequencing was a slow, laborious process. However, in the 1970s, the pace of discovery heated up (automated sequencing, oncogenes), and this increased ever faster over the next 3-4 decades. The 1980s represented the “inflection point” of discovery into the causes of cancer. By the end of the 1980s, the concept of multistep carcinogenesis driven by “alterations” in the genome was advanced by Vogelstein's lab at Johns Hopkins.

Alfred Knudson in 1971, based upon studies of familial and sporadic retinoblastoma (RB) that two copies of a gene related to this disease had to be disabled in the evolution of RB, and that individuals with the familial form of RB had a germline mutation in that gene, which accounted for the increased risk and early onset. This set the stage for the appearance of techniques to prove the concept.

In the 1970s, familial adenomatous polyposis (FAP), Peutz-Jeghers Syndrome (PJS) and juvenile polyposis syndrome (JPS) were recognized as distinctive clinical phenotypes, and occurred on a familial basis. Actually, this first required the standardized pathological interpretation of colonic and intestinal polyps. Then, in 1986 Lemuel Herrera, a surgeon at Roswell Park in Buffalo, identified a patient with multiple congenital abnormalities and “Gardner's Syndrome” (FAP), which his family did not have. He asked his colleague Avery Sandberg to do chromosomal analysis, which led to the discovery of a microscopically visible interstitial deletion on 5q. They accurately proposed that this represented the loss of multiple genes on 5q, leading to a complex (and unique) phenotype, and that one of those genes deleted was connected to FAP. In 1987, Walter Bodmer's lab in London used restriction fragment length polymorphism (RFLP) analysis and linked families with FAP to the 5q locus. Moreover, they showed losses on 5q in 20% of sporadic colorectal cancers (CRCs).

This resonated with the Knudson hypothesis and suggested that a gene responsible for FAP would be on chr 5q21-22, but it took four years and the collaboration of several labs to finally clone the APC gene in 1991. The function of the gene was a complete surprise, as it played a central role in the WNT growth-regulatory pathway. The APC gene was also the 5q event that Vogelstein placed at the beginning of the multistep carcinogenesis model of 1990. These early days were largely driven by techniques that could identify genetic losses in tumor DNA.

The discovery of microsatellite instability (MSI) and its link to Lynch Syndrome (LS) came as lightning strike in 1993. Many labs were looking for the losses of tumor suppressor genes (TSGs) in cancers using RFLPs, and then extended the analyses by using variable number tandem repeats (VNTRs) and microsatellites (simple VNTRs with cassettes of 1-4 nucleotides), both of which are widespread throughout the human genome and valuable for genomic mapping. In 1992, Perucho (in San Diego) used “arbitrarily-primed PCR” to generate a large number of PCR products from DNA, separated them on PAGE gels, and compared results from CRCs with the patient's normal DNA to look for allelic losses (or gains), which would then lead to TSGs (or oncogenes) involved in carcinogenesis. However, his careful eye noted that some of the differences between the AP-PCR products from cancers and normal DNA represented band shifts, due to a small change in the length of the PCR product in cancer. He sequenced the altered bands, and discovered deletions (or insertions) in microsatellite sequences that were very widespread in a subset of the cancers, but not present in most other CRCs. He proposed that this was a unique “pathway” to carcinogenesis for ~15% of CRCs, but had a hard time convincing reviewers of this novel concept. While he was trying to get his findings published, Steve Thibodeau discovered the same thing at the Mayo Clinic. At the same time, Lauri Aaltonen (Finland; part of the Vogelstein-de la Chapelle collaboration) used a microsatellite marker (D2S123) located on chr 2p and found significant linkage between this locus and Lynch Syndrome (LS). Microsatellites markers were then used to look for TSG losses on 2p21 and elsewhere. Instead, MSI was recognized, and suddenly there were 3 groups with the same discovery published in May and June of 1993.

The three groups who found MSI published their odd-looking autoradiographs in Science and Nature, but none of the human geneticists immediately recognized the implications. However, those who had been working in basic yeast genetics for years (Richard Kolodner, Rick Fishel, Paul Modrich, Thomas Petes, Michael Liskay and others) recognized that this probably represented loss of the DNA mismatch repair (MMR) system in the tumors, which would represent a totally unique mechanistic basis for this subset of about 15% of CRCs. In May, 1993, by coincidence, Kolodner's group at Dana Farber in Boston had just cloned the hMSH2 gene based upon its similarity to the yeast MSH2 gene, but they had to identify pedigrees with LS and find a germline mutation to make their point. The human geneticists had the families and familiarity with the human genome (organized differently than in yeast), and soon suspected DNA MMR genes themselves. The race was on, and by December 1993, both groups linked LS to germline mutations in hMSH2, and reported this in Cell; Kolodner won the race by 2 weeks, although he mistook a simple SNP for the mutation The Vogelstein-de la Chapelle collaboration cloned the hMSH2 gene, found mutations in families, and found a cell line with MSI (which happened not to have an MSH2 mutation; rather it was mutated at the hMLH1 locus, reported in a few months). What is notable is how quickly this story went from the empirical observation of MSI to the cloning of the familial CRC genes.

The pace of discovery continued to be astonishing, and both Kolodner's and the Vogelstein-de la Chapelle groups found germline mutations in the hMLH1 gene in other LS families—published on consecutive days in Nature and Science on March 17 and 18, 1994. Kolodner used hybridization techniques to find hMLH1 based upon the yeast MLH sequence, but Vogelstein's group also used bioinformatics approaches to find not only hMLH1, but 2 more yeast MLH homologs, hPMS1 and hPMS2. hPMS2 turned out to be a legitimate LS gene; hPMS1 did not. The LS story had a long tail after this initial cluster of reports; hMSH6 was initially cloned by Vogelstein and Jiricny in June 1995, but not linked to LS families until Miyaki did so in November 1997. EPCAM was linked to some MSH2-like LS families in 2006. It would be an understatement to say that this led to a subsequent series of insights into how the DNA MMR system works, and what happens when this system is disabled.

The 21st Century has provided ongoing broad insight into gut development and carcinogenesis in the context of both WNT signaling and DNA MMR. Most colorectal neoplasms begin by disabling the WNT pathway that regulates epithelial proliferation. It is now appreciated that about 15-20% of CRCs are hypermutated though the inactivation of both MMR genes and (less often) DNA polymerase proofreading subunits, and develop through a unique pathway of “target” genes, that they grow and evolve differently, have different clinical behaviors, and respond differently to oncological treatment. Tumors with MSI do not respond to classical cytotoxic chemotherapy (unlike non-MSI CRCs), but do respond to immune checkpoint therapies—to which non-MSI tumors are non-responsive. Moreover, we now have panel that test for multiple genes for any of the hereditary cancer syndromes.

Finally the genes for PJS, JPS, Cowden's Disease (CD) and Bannayan-Riley Ruvalcaba Syndrome (BRRS) were all discovered by variations on positional cloning, but with less notoriety. Whereas PJS has a classic phenotype that has been linked to just one gene (LKB1/STK11), JPS has been a much more problematic disease because of the clinical heterogeneity of the phenotype generally and clinical overlap with CD and BRRS. Several genes have been linked to JPS, but this disease is still confusing. There are probably several diseases that we call JPS, which confuses the genetics. SMAD4, BMPR1A, SMAD9, and other genes have all been linked to JPS. Even Cowden's Disease, linked to the PTEN gene, can present with hyperplastic or hamartomatous polyps. BRRS may be a pediatric variant of CD.

At this time, there are candidate genes for almost all of the familial polyposis genes, from APC to POLD1 and POLE (Polymerase Proofreading Associated Polyposis), to the recessive polyposis genes, MutYH and NTHL1. However, there are families with these phenotypes in which no genetic diagnosis can be made. Biallelic MMR gene mutations, or constitutional mismatch repair deficiency syndrome—CMMRDS—can present with colonic polyposis in childhood. Finally, the serrated polyposis syndrome with multiple polyps that look a bit like hyperplastic polyps is rarely familial, is linked to another CRC phenotype (CpG island methylator phenotype or CIMP), and is the final outlier without any consensus germline mutations causing the syndrome.

Citation Format: C. Richard Boland. The discovery of the hereditary colorectal cancer genes: A historical perspective. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr IA02.

Clinical significance of SNORA42 as an oncogene and a prognostic biomarker in colorectal cancer

PURPOSE

Despite recent advances in colorectal cancer (CRC) treatment, the prognosis of patients suffering from this malignancy still remains substandard, and metastatic recurrence following curative surgery is the leading cause of mortality. Therefore, it is imperative to identify prognostic markers to predict the clinical outcome of CRC patients. Recent evidence revealed the new role of small nucleolar RNAs (snoRNAs) in oncogenesis. Herein, we systematically evaluated dysregulation of snoRNAs in CRC and clarified their biomarker potential and biological significance in CRC.

EXPERIMENTAL DESIGN

We analysed expression levels of 4 snoRNAs in 274 colorectal tissues from 3 independent cohorts and 6 colon cancer cell lines. The functional characterisation for the role of SNORA42 in CRC was investigated through a series of in vitro and in vivo experiments.

RESULTS

In the screening phase, expression levels of all four snoRNAs were significantly elevated in CRC tissues than in corresponding normal mucosa. In the clinical validation cohort, increased SNORA42 expression was an independent prognostic factor for overall survival and disease-free survival, and was a risk factor for distant metastasis. SNORA42 expression negatively correlated with overall survival in an additional independent cohort and identified the patients with high risk for recurrence and poor prognosis in stage II CRC. Furthermore, in vitro and in vivo analyses showed that SNORA42 overexpression resulted in enhanced cell proliferation, migration, invasion, anoikis resistance and tumorigenicity.

CONCLUSIONS

SNORA42 appears to be a novel oncogene and could serve as a promising predictive biomarker for recurrence and prognosis in patients with CRC.

Recommendations on Fecal Immunochemical Testing to Screen for Colorectal Neoplasia: A Consensus Statement by the US Multi-Society Task Force on Colorectal Cancer

The use of the fecal occult blood test (FOBT) for colorectal cancer (CRC) screening is supported by randomized trials demonstrating effectiveness in cancer prevention and widely recommended by guidelines for this purpose. The fecal immunochemical test (FIT), as a direct measure of human hemoglobin in stool has a number of advantages relative to conventional FOBT and is increasingly used relative to that test. This review summarizes current evidence for FIT in colorectal neoplasia detection and the comparative effectiveness of FIT relative to other commonly used CRC screening modalities. Based on evidence, guidance statements on FIT application were developed and quality metrics for program implementation proposed.