Actor Chadwick Boseman, best known for his title role as King T’Challa in the movie “Black Panther,” died last weekend at the age of 43 from colon cancer. An Instagram post on his account by his family read:
“Chadwick was diagnosed with stage III colon cancer in 2016 and battled with it these last 4 years as it progressed to stage IV. A true fighter, Chadwick persevered through it all, and brought you many of the films you have come to love so much. From Marshall to Da 5 Bloods, August Wilson’s Ma Rainey’s Black Bottom and several more, all were filmed during and between countless surgeries and chemotherapy.”
Besides playing a superhero in the Marvel Universe, Boseman was known for the iconic Black characters he played in biopic movies: Jackie Robinson in “42,” James Brown in “Get on Up,” and Thurgood Marshall in “Marshall.”
Boseman was also a political activist, often speaking about his experiences with racism while growing up. He realized his celebrity gave him a platform to speak against racial injustice and he used it frequently.
After the shocking news of his death, condolences to his family and accolades for his work exploded on social media. Messages from Marvel Universe co-stars Chris Evans, Robert Downey Jr., and Angela Bassett mixed with those of Martin Luther King III, Oprah Winfrey, and fellow Howard alumna Kamala Harris sang his praises. Presidential nominee Joe Biden said Boseman “inspired generations and showed them they can be anything they want — even super heroes.”
Colorectal Cancer in Black Americans
Colorectal cancer (CRC) is currently the fourth most common cancer in the United States. The National Cancer Institute estimates that in 2020 there will be 104,610 new cases of colon cancer and 43,340 cases of rectal cancer. There will be about 53,200 deaths from CRC.
Black Americans have the highest incidence and mortality rates of CRC of any ethnic group in the U.S. According to National Cancer Institute Statistics, Epidemiology, and End Results (SEER) data, the incidence of CRC in Black people is 20% higher than in whites, and mortality rates are 35% higher.
Some of this disparity can be explained by differences in access to care, lower screening rates, cultural mistrust of the medical community, and a high burden of cancer risk factors.
However, disparities persist, even when adjustments are made for these factors. Researchers are now examining the role of “ethnicity-specific factors, including genetic and environmental factors relating to risk of CRC, the biology of CRC progression, and the changes in screening and mortality.”
Factors Involved in Increased CRC Risk in Black People
Socioeconomic and Psychosocial Barriers
There are many socioeconomic and psychologic barriers that contribute to the disparity in CRC in Black people. Black patients are ethnically and linguistically diverse and may belong to low-education and low-income groups. Access to healthcare may be limited due to lack of income, lack of health insurance, inability to afford taking time away from work for doctor visits, lack of transportation, and lack of childcare.
Psychosocial barriers include lack of information, fear of cancer diagnosis, feeling too busy to take the time, distrust of doctors, and low perceived risk of CRC.
Colorectal Cancer Screening
Over the past several years, increased CRC screening has led to a decrease in the incidence of CRC due to the removal of precancerous polyps. According to SEER data, whites have seen a decrease in CRC incidence since the 1990s, but the incidence of CRC in African Americans began to decrease only in the early 2000s.
Black people have a significantly lower incidence of CRC screening compared with other ethnic groups. The CDC reports that during 2000-2015 among adults age 50-75, CRC screening percentages more than doubled for non-Hispanic Black, Hispanic, and non-Hispanic Asian adults.
Despite these increases in 2015, however, the prevalence of colorectal cancer screening was higher among non-Hispanic white (65.6%) adults than among non-Hispanic Black (60.3%), non-Hispanic Asian (52.1%), and Hispanic (47.4%) adults.
The American College of Gastroenterology recommends colonoscopy screening as the preferred method of CRC screening, stating that colonoscopy prevents as well as detects the disease.
Stool-based tests such as the fecal immunochemical test and the guaiac-based fecal occult blood test detect blood in the stool, which can be caused by bleeding from cancerous polyps. A stool DNA test (Cologuard) is also available and is used to detect certain abnormal DNA sequences for cancer or polyp cells as well as for hidden blood. All three of the stool-based tests can be performed at home, which may be a benefit for patients with some of the above barriers.
Location of Lesions
Despite the overall decrease in the incidence of CRC, there has been an increase in CRC found in the proximal colon (right side of the colon) across all ethnic groups. In addition, studies have shown that the incidence of proximal colonic tumors is disproportionally higher in the Black community. Proximal colonic tumors have been associated with a worse prognosis than distal colonic lesions.
Relationship to Age
As with the location of CRC, there has also been a shift of CRC to younger patients in all racial/ethnic groups under age 50. And once again, this shift appears to affect the Black population more than other groups.
A review of almost 30,000 patients with young-onset CRC found that survival after CRC diagnosis at a young age was significantly lower among non-Hispanic Black people compared with non-Hispanic whites, even among patients with early-stage disease.
This skew of incidence and poorer outcome of CRC in younger Black patients has caused several groups to change the age for CRC screening in Black people. The American Gastroenterological Association and the American Society of Colon and Rectal Surgeons now recommend that Black people be screened starting at age 45, while the American College of Physicians recommends age 40.
Genetic Risk Factors
It is estimated that genetic factors may contribute as much as 35% to the overall risk of CRC. Several specific genetic mutations have been associated with an increased risk of CRC. For example, mutations in the adenomatous polyposis coli (APC) gene are linked to familial adenomatous polyposis. The KRAS, SMADs, and TP53 mutations have been found in adenomatous polyps. Lynch syndrome, the most common hereditary CRC syndrome, is associated with mutations in the DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2.
Black populations with hereditary forms of CRC have harbored novel mutations in the MMR genes, and other genetic mutations have been found in the APC, MUTYH, and MMR genes in the African American population.
Single-nucleotide polymorphisms (SNPs) are common genetic variations. Genome-wide association studies examine the frequency of how often particular SNPs are associated with any specific disease — in this case CRC. There is a growing body of evidence associating particular SNPs with CRC in European-ancestry CRC cases compared with controls. The number of studies looking at African American subjects is small, however, so only time will tell whether this method will reveal significant associations in the Black population.
Other Possible Factors
Other factors are just beginning to be evaluated as causes in the disparity of CRC incidence and mortality in Black individuals. This includes the role of diet and differences in gut microbiome, vitamin D levels, and the incidences of obesity and diabetes.
Researchers are also starting to look at whether carcinogenic mechanisms, such as microsatellite instability, somatic mutations, epigenetic changes, and CRC-specific gene dysregulation play roles in CRC in the Black population.
Michele R. Berman, MD, and Mark S. Boguski, MD, PhD, are a wife and husband team of physicians who have trained and taught at some of the top medical schools in the country, including Harvard, Johns Hopkins, and Washington University in St. Louis. Their mission is both a journalistic and educational one: to report on common diseases affecting uncommon people and summarize the evidence-based medicine behind the headlines.