Abstract IA05: Epidemiologic, environmental, and molecular disparities in gastrointestinal cancer among Hispanics
Authors: Cruz-Correa Marcia 
Published: March 2017

Colorectal Cancer. In the United States (US), CRC is the most diagnosed gastrointestinal cancer. Despite increasing adherence to routine screening and advances in therapeutic strategies, it has been estimated that approximately 134,490 cases of CRC will be diagnosed and close to 50,000 deaths due to this disease will be reported in 2016 in the US. CRC disease burden varies dramatically between races and ethnicities for reasons that remain incompletely understood. African Americans (AA) have the highest CRC incidence and the lowest survival rates compared to other racial/ethnic groups. When compared to non-Hispanic Whites (NHW), US mainland Hispanics (USH) present more advanced disease and have worse survival. Furthermore, significant differences in cancer incidence patterns and tumor characteristics have been reported among USH. A combination of factors, which may include barriers to healthcare, environmental factors, and/or genetic/molecular factors, are thought to contribute to the racial/ethnic disparities observed.

Environmental factors such as diet and the microbiome have been implicated in colorectal carcinogenesis. Differences in the the intake of micro- as well as macronutrients was documented among AA and NHW suggesting that associations between diet and CRC might differ between the two racial groups, possibly as a result of diet-driven changes in the gut microbiota composition that increase cancer risk. Advances in molecular biology in the last three decades have helped elucidate some of the mechanisms leading to colorectal carcinogenesis. Non-familial, sporadic CRC is a result of three major molecular mechanisms: microsatellite instability (MSI), chromosomal instability (CIN), and the CpG island methylator phenotype (CIMP). AA have been reported to have a higher incidence of MSI, CIMP, and proximal tumors, with CRC occurring at a younger age and with more advanced staging, compared to the general population. During the last decade, an increase in early-onset CRC (&lt;50 years) was observed to be markedly greater among Hispanics compared to NHW (27%) and AA (15%). Hispanics with CRC are diagnosed with more advanced disease and have worse survival compared to NHW.

Gastric Cancer. Despite the overall decrease in the incidence of GC since the 1930s, In the US, the American Cancer Society estimates that in 2016 26,370 new cases of GC will be diagnosed and approximately 10,730 individuals will die from this type of cancer. GC incidence rates are vary dramatically across different countries and are higher in less developed countries. The risk factors for the development of gastric cancer include: being male, older age, Helicobacter pylori infection, tobacco smoking, diet, living in places with high altitude, low socioeconomic status, and being part of the Asian, Hispanic, and African American communities. H. pylori is a major risk factor for GC, specifically non-cardia GC. Prevalence of H. pylori infection is also influenced by socioeconomic, demographic, and racial/ethnic factors. Among middle-aged adults, the prevalence is over 80% in developing countries and 20-50% in industrialized countries. The estimated prevalence of H. pylori in the US is 30.7%; however, it is highly variable between racial/ethnic groups. H. pylori prevalence was reported to be 21% in NHW, 52% in African-Americans, and 64% in Mexican-Americans. Marked differences in H. pylori status have been reported among Hispanic individuals from different regions of central and South America.

Although GC incidence and mortality has been steadily declining, significant geographical and racial/ethnic health disparities continue to be observed. The observed decline in GC incidence is more notable in non-cardia tumors, which are mostly attributable to H. pylori, smoking, and high salt diets. Asians, Hispanics and AA have been reported to have a higher proportion of distal GC (tumors in the body, antrum, and pylorus) compared to NHW, which are most commonly diagnosed with proximal GC (tumors in the cardia and fundus). In the US, GC represents a marked health disparity where non-whites, including Hispanics, have nearly 2-fold higher incidence rates, for reasons that remain largely uninvestigated. A significantly higher incidence of GC has been observed among Asians, followed by AA and Hispanics compared to NHW. Overall 3-year survival was reported to be highest among Asians (26%), followed by AA; Hispanics and NHW had comparable survival rates (~19%). Latin America has a significant GC burden, with a concentration of disease in the mountainous regions of the Pacific littoral zone, where the mortality-to-incidence ratio is extremely high at 0.82. Patients of Indian, Hispanic, and Asian ancestry had been found to have significantly higher prevalence rates of H. pylori gastritis, GIM, and gastric atrophy compared to other racial/groups in the US. The prevalence of GIM among different racial/ethnic groups did not correlate with H. pylori prevalence, but did significantly correlate with GC incidence in the patients' ancestral countries. However, the factors that contribute to the disproportionate CRC and GC disease burden among races/ethnicities are yet to be fully elucidated. During the presentation we will discuss epidemiological, molecular and environmental disparities associated with colorectal and gastric cancer and review current research efforts in at risk populations.

Citation Format: Marcia Cruz-Correa. Epidemiologic, environmental, and molecular disparities in gastrointestinal cancer among Hispanics. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr IA05.