Microbiome and colorectal carcinogenesis:Linked mechanisms and racial differences

Various studies have shown the interplay between the intestinal microbiome,environmental factors,and genetic changes in colorectal cancer(CRC)development.In this review,we highlight the various gut and oral microbiota associated with CRC and colorectal adenomas,and their proposed molecular mechanisms in relation to the processes of“the hallmarks of cancer”,and differences in microbial diversity and abundance between race/ethnicity.Patients with CRC showed increased levels of Bacteroides,Prevotella,Escherichia coli,enterotoxigenic Bacteroides fragilis,Streptococcus gallolyticus,Enterococcus faecalis,Fusobacterium nucleatum(F.nucleatum)and Clostridium difficile.Higher levels of Bacteroides have been found in African American(AA)compared to Caucasian American(CA)patients.Pro-inflammatory bacteria such as F.nucleatum and Enterobacter species were significantly higher in AAs.Also,AA patients have been shown to have decreased microbial diversity compared to CA patients.Some studies have shown that using microbiome profiles in conjunction with certain risk factors such as age,race and body mass index may help predict healthy colon vs one with adenomas or carcinomas.Periodontitis is one of the most common bacterial infections in humans and is more prevalent in Non-Hispanic-Blacks as compared to Non-Hispanic Whites.This condition causes increased systemic inflammation,immune dysregulation,gut microbiota dysbiosis and thereby possibly influencing colorectal carcinogenesis.Periodontal-associated bacteria such as Fusobacterium,Prevotella,Bacteroides and Porphyromonas have been found in CRC tissues and in feces of CRC patients.Therefore,a deeper understanding of the association between oral and gastrointestinal bacterial profile,in addition to identifying prevalent bacteria in patients with CRC and the differences observed in ethnicity/race,may play a pivotal role in predicting incidence,prognosis,and lead to the development of new treatments.

Confounders in Adenoma Detection at Initial Screening Colonoscopy: A Factor in the Assessment of Racial Disparities as a Risk for Colon Cancer

Background and Aims: The incidence and mortality of colorectal cancer is persistently highest in Black/African-Americans in the United States. While access to care, barriers to screening, and poverty might explain these findings, there in increased interest in examining biological factors that impact the colonic environment. Our group is examining biologic factors that contribute to disparities in development of adenomas prospectively. In preparation for this and to characterize a potential patient population, we conducted a retrospective review of initial screening colonoscopies in a cohort of patients. Methods: A retrospective review was performed on initial average risk screening colonoscopies on patients (age 45 - 75 years) during 2012 at three institutions. Descriptive statistics and multivariable logistic regression models were used to examine the relationship between potential risk factors and the detection of adenomas. Results: Of the 2225 initial screening colonoscopies 1495 (67.2%) were performed on Black/African-Americans and 566 (25.4%) on Caucasians. Multivariable logistic regression revealed that older age, male sex, current smoking and teaching gastroenterologists were associated with higher detection of adenomas and these were less prevalent among Black/African-Americas except for age. Neither race, ethnicity, BMI, diabetes mellitus, HIV nor insurance was associated with adenoma detection. Conclusion: In this sample, there was no association between race and adenoma detection. While this may be due to a lower prevalence of risk factors for adenomas in this sample, our findings were confounded by a lower detection rate by consultant gastroenterologists at one institution. The study allowed us to rectify the problem and characterize patients for future trials.