Excess of Proximal Microsatellite-Stable Colorectal Cancer in African Americans from a Multiethnic Study

Abstract

Purpose African Americans (AAs) have the highest incidence of colorectal cancer (CRC) compared to other US populations and more proximal CRCs. The objective is to elucidate the basis of these cancer disparities. . Experimental design 566 AA and 328 Non-Hispanic White (NHW) CRCs were ascertained in five Chicago hospitals. Clinical and exposure data were collected. Microsatellite instability and BRAF (V600E) and KRAS mutations were tested. Statistical significance of categorical variables was tested by Fisher's exact test or logistic regression and age by Mann-Whitney U test. Results Over a ten-year period, the median age at diagnosis significantly decreased for both AAs (68 to 61; P<0.01) and NHWs (64.5 to 62; P=0.04); more AA patients were diagnosed before age 50 than NHWs (22% vs 15%; P=0.01). AAs had more proximal CRC than NHWs (49.5% vs. 33.7%; P<0.01), but overall frequencies of microsatellite instability, BRAF and KRAS mutations were not different nor were they different by location in the colon. Proximal CRCs often presented with lymphocytic infiltrate (P<0.01) and were diagnosed at older ages (P=0.02). Smoking, drinking, and obesity were less common in this group, but results were not statistically significant. Conclusions Patients with CRC have gotten progressively younger. The excess of CRC in AAs predominantly consists of more proximal, microsatellite stable tumors, commonly presenting lymphocytic infiltrate and less often associated with toxic exposures or a higher BMI. Younger AAs had more distal CRCs than older ones. These data suggest two different mechanisms driving younger age and proximal location of CRCs in AAs.

Race-dependent association of sulfidogenic bacteria with colorectal cancer

“…26 The parent study received approval for human subjects research from the institutional review boards (IRBs) of each participating medical centre; the parent protocol was administered by the IRB at University of Illinois Hospital and Health Sciences System (2010–0168). Colonic tissue biopsies from uninvolved or healthy mucosa were studied from 329 subjects after routine bowel preparation.…”

“…Persons with a personal history of cancer, IBD, adenomatous or benign polyps, polyposis or tumours with microsatellite instability were excluded. 26 Clinical data were extracted from medical records, and epidemiological and demographic information were obtained using subject questionnaires as previously described. 26 Factors analysed included age, sex, race; tumour or biopsy site, tumour stage; body weight, body mass index (BMI); education and income level; usage of tobacco products and alcohol; and usage of omega-3 fatty acids and non-steroidal anti-inflammatory drugs (NSAIDs) (table 1 and online supplementary table S1).…”

Racial Disparity in Gastrointestinal Cancer Risk

“…Additionally, Blacks show a higher proportion of both high risk adenomas and CRC in the proximal colon [4,75,82,83], a 7–15% more right colon distribution than NHWs. Proximal colon polyps, in particular, may be harder to spot at colonoscopy, and the reduction from CRC mortality with colonosocpy is lower than the left side of the colon [84–86], potentially amplifying the disparity.…”

Effects of high-fat diet on 1,2-dimethylhydrazine-induced aberrant crypt foci and colorectal tumours in rats

“…African-Americans have experienced an increased incidence of CRC compared to other U.S. populations. In addition, the prevalence of proximal CRC is higher among African-Americans and the average age for the onset of CRC is becoming younger (5). CRC is one of the common malignancies in China.…”