The aim of this submission is to develop a quantitative microRNA assay for screening right and left colon cancer in stool of patients, particularly at the early adenoma stage (e.g., polyps 3 1 cm with high grade dysplasia), which shows higher sensitivity than FOBT, and results in better compliance &is more economical than invasive colonoscopy. We studied the expression of 15 mature miRNAs by stem-loop RT primers and TaqMan minor grove binding probes in stool and tissue of 30 individuals (5 normal, 10 IBD &15 with colon cancer). Several miRNAs showed preferential expression in stool and tissue, which was more pronounced in later CRC Dukes'stages. Based on these significant and published results, we propose a randomized nested case-control study to test the 15 miRNAs blindly in stool of 60 individuals chosen randomly from 500 subjects [20 controls &40 CRC patients {20 precancerous polyps (stage 0-1), and 20 colon cancer (stages 2 to 4)}]. To establish clinical sensitivity and specificity, the miRNA results will be correlated with colonoscopy, FOBT and pathology data. A numerical underpinning of the method will be derived from cytological and molecular methods on isolated colonocytes and stool to determine the fraction of transformed miRNA as a function of total mRNA expression. Standardization will establish test's performance criteria (optimal sampling preparation, preservation, storage &running conditions) to ensure that the assay will perform the same way in any Lab., by any trained personnel. Success in this step will be followed by a validation study on larger sample. In 1993 it was envisioned that population-based colorectal cancer (CRC) screening had arrived (1). Sixteen years later we have not yet achieved the goal of screening most of the eligible USA population despite the availability of multiple screening tests. In the USA, colorectal cancer (CRC) considered the second and third most common malignancy in and women, respectively, represents 10% of incident cancers and cancer deaths. About 6% of the population will develop CRC in their lifetime. In 2007, 153,760 new cases and 52,180 deaths were estimated (2). Globally, there are about 1 million new cases and about 500,000 deaths per year (3), and these numbers are destined to increase because of worldwide adoption of a Western-type diet (4). CRC is the third leading cause of cancer death among white, African American, Asian/Pacific Islander and Indian/Alaska Native men, but second among Hispanic men in the USA (5). CRC incidence has declined from about 60 per 100,000 in 1975 to ~ 50 per 100,000 in 2004, and the decrease in USA mortality has recently accelerated (i.e., the rate decreased from about 29 per 100,000 population in 1970 to about 18 per 100,000 in 2004, with similar decline for white men and women, although the decline for men began several years after women), but it has changed little for African American men and women. Since 1990, the mortality in African Americans has decreased from about 30 to 25 per 100,000 populations, with higher mortality in men than women, and since about 1980 the mortality has been higher in African Americans than whites. Five-year survival rates are strikingly different by stage ranging from 90% for localized disease to 10% for distant disease, clearly arguing for early detection (5). The guaiac-based fecal occult blood test is the only screening test proved to be effective in reducing CRC mortality by three randomized clinical trials (RCTs) (6-8). Other tests such as an immunochemical (IMC)-based fecal blood test although never tested in a RCT, have been evaluated against guaiac-based tests and have performed at least as well with higher compliance rates (9-13). CRC is the only cancer for which the diagnostic test colonoscopy, considered to be the gold standard, is recommended as a screening test (14.15). There are several other methods available for colon cancer screening [e.g., flexible sigmoidoscopy (16), CT colonography (virtual colonoscopy) (17), capsule endoscopy (18), double contrast barium enema (19), molecular DNA tests in stool and blood (20-25);however, none is optimal, and with poor rates in some segments of the population (26,27). Recently, there has been an increase in the number of lesions arising from more proximal regions of the colon, and increasing incidence of right sided CRC lesions has been reported with increasing age (28,29), necessitating the use of flexible, fiber optic sigmoidoscopes. However, colonoscopy screening for the 70 million people older than 50 years of age in the USA could cost $10 billion per year and exceed the physician capacity to perform this procedure (30,31). Clearly, a simple, inexpensive, noninvasive, sensitive and specific screening test is needed to identify people at risk for developing advanced adenomas or CRC who would benefit from subsequent colonoscopy. Current participation rates in CRC screening are less than 30% for both genders, compared to rates of 70 to 80% for breast and cervical cancer screening, respectively (32). Participation could be enhanced by use of molecular tests that are less uncomfortable, less expensive and offer greater accuracy (more sensitivity and specificity). However, larger well designed clinical studies are needed to corroborate initial results.
Public Health Relevance (Narrative Statement) Mortality and morbidity from colorectal cancer (CRC) represent major health care problems involving a malignant disease that is theoretically preventable through appropriate screening. Early detection would be greatly enhanced if accurate, practical and cost effective diagnostic biomarkers for this malignancy were available. Current screening methods lack sensitivity (e.g., fecal occult blood test, FOBT), costly and have low compliance (e.g., colonoscopy). Our preliminary data shows that quantitative changes in the expression of few microRNA genes associated with colon cancer permit development of more sensitive and specific CRC molecular markers than those currently available for a cancer that is deadly if not diagnosed before metastasis. A microRNA approach is preferable to a DNA-, epigenetic-, proteomic-, or an mRNA-based test. If performance criteria are met, as proposed in this undertaking, the non-invasive micoRNA test in stool would be advanced to the clinical setting and will make a significant impact on the preventive oncology of CRC.
| Ahmed, Farid E; Ahmed, Nancy C; Vos, Paul W et al. (2013) Diagnostic microRNA markers to screen for sporadic human colon cancer in stool: I. Proof of principle. Cancer Genomics Proteomics 10:93-113 |
