Recently a close relative of mine was diagnosed with advanced colon cancer. The experience has been at once saddening, terrifying and sobering. Why did this happen? How did it happen? Why wasn’t it caught earlier? From an objective perspective, the case is unusual on a number of fronts, and illuminates the major limitations of the current state-of-art of colon cancer screening.
1. Ethnicity. Like myself, my uncle-in-law is of Indian descent. Colon cancer is much less common in Asian ethnicities than Western ones. In Japan, where the best data is available, the disease is uncommon enough that doctors do not routinely perform colon cancer screening (in contrast they routinely screen for stomach cancer, which we don’t do in the U.S.). The risks and benefits of screening for a disease are related to its prevalence. Though my uncle is 53, three years beyond the age at which screening is routinely recommended in the United States, I would not have necessarily recommended it for him given its low prevalence in India.
2. Age: Even for people living in the U.S., developing advanced colon cancer at 53 is rare. Though screening is recommended for average-risk individuals starting at age 50, the average age at diagnosis is 64. The goal of screening is to detect and remove pre-cancers before they progress into cancer or if cancer has already developed to catch it early at a curable stage. Thus had we screened my uncle-in-law for colon cancer we would be expecting, if anything, to find precancerous polyps, not full-blown cancer.
3. Family history: Every American over ages 50 to 75 needs to be screened for colon cancer, regardless of lack of family history.1 In those with a family history, screening may need to begin at an earlier age. For example, experts recommend screening first-degree relatives of people who developed cancer before age 60 starting at age 40 or 10 years before the age of diagnosis, whichever comes first.2 As far as we know, there is no history of colon cancer in our extended family. Such a history may have tipped us off to begin our prevention efforts earlier.
Our understanding of cancer and other diseases is still limited, and as a result our abilities to detect diseases early and to prevent them altogether are still crude. Most diseases result from a combination of genes and environmental exposure. The better our understanding of these elements the greater our ability for targeted prevention. Family history of colon cancer is a proxy for our genetic makeup. Thus people with a history of colon cancer in first-degree relatives with whom we share 50% of our genes or in multiple second degree relatives are at higher risk than the average person. Ethnicity is another proxy for genetic risk and one that is even more crude. In the future, we will hopefully be able to move beyond these blunt measures and better assess genetic risk. Such understanding would allow us to better target screening to those at highest risk. This would prevent unnecessary testing in low-risk adults and promote screening in people at truly increased risk. Already in diabetes researchers have identified specific genetic variants that predispose people to diabetes; in oncology, BRCA1 and BRCA2 are already being used in the clinics to identify women at very high risk of breast and ovarian cancers.
Our environment also contributes to our risk of colon cancer. Population studies have demonstrated that as people immigrate from Japan to the United States their risk of colon cancer increases. Such “natural experiments” provide strong evidence that something about our Western way of life predisposes us to colon cancer, but the exact reasons are still unclear. Though some have suggested that high fat, low fiber diets may play a role, these data have not established causality. Contrast this degree of understanding with cervical or lung cancer. In cervical cancer we have established that the cause of the disease is infection with the human papillomavirus or HPV; this understanding has led to the development of the first vaccine against cancer. Likewise, while it is easy to take for granted today, the knowledge that smoking is the major risk factor for lung cancer has had enormous implications and saved countless lives. Hopefully one day we will learn more about the modifiable risk factors for colon cancer and be able to prevent it altogether.
Given these limitations, it’s remarkable to consider that our current state-of-art — routinely screening all Americans over age 50 with fecal occult blood testing, sigmoidoscopy or colonoscopy — is proven to reduce death from colon cancer by 33%. If we simply increased the proportion of Americans being screened today to 90%, we would prevent 19,000 deaths annually.3 Still, tragedies like the one in my family are a harsh reminder that while we have made much progress we have much farther to go.
- Shantanu Nundy, M.D.
1 http://www.ahrq.gov/clinic/uspstf08/colocancer/colosum.htm
2 http://caonline.amcancersoc.org/cgi/content/full/CA.2007.0018v1
3 http://www.prevent.org/content/view/50/120/
Recently a close relative of mine was diagnosed with advanced colon cancer. The experience has been at once saddening, terrifying and sobering. Why did this happen? How did it happen? Why wasn’t it caught earlier? From an objective perspective, the case is unusual on a number of fronts, and illuminates the major limitations of the current state-of-art of colon cancer screening.
1. Ethnicity. Like myself, my uncle-in-law is of Indian descent. Colon cancer is much less common in Asian ethnicities than Western ones. In Japan, where the best data is available, the disease is uncommon enough that doctors do not routinely perform colon cancer screening (in contrast they routinely screen for stomach cancer, which we don’t do in the U.S.). The risks and benefits of screening for a disease are related to its prevalence. Though my uncle is 53, three years beyond the age at which screening is routinely recommended in the United States, I would not have necessarily recommended it for him given its low prevalence in India.
2. Age: Even for people living in the U.S., developing advanced colon cancer at 53 is rare. Though screening is recommended for average-risk individuals starting at age 50, the average age at diagnosis is 64. The goal of screening is to detect and remove pre-cancers before they progress into cancer or if cancer has already developed to catch it early at a curable stage. Thus had we screened my uncle-in-law for colon cancer we would be expecting, if anything, to find precancerous polyps, not full-blown cancer.
3. Family history: Every American over ages 50 to 75 needs to be screened for colon cancer, regardless of lack of family history.1 In those with a family history, screening may need to begin at an earlier age. For example, experts recommend screening first-degree relatives of people who developed cancer before age 60 starting at age 40 or 10 years before the age of diagnosis, whichever comes first.2 As far as we know, there is no history of colon cancer in our extended family. Such a history may have tipped us off to begin our prevention efforts earlier.
Our understanding of cancer and other diseases is still limited, and as a result our abilities to detect diseases early and to prevent them altogether are still crude. Most diseases result from a combination of genes and environmental exposure. The better our understanding of these elements the greater our ability for targeted prevention. Family history of colon cancer is a proxy for our genetic makeup. Thus people with a history of colon cancer in first-degree relatives with whom we share 50% of our genes or in multiple second degree relatives are at higher risk than the average person. Ethnicity is another proxy for genetic risk and one that is even more crude. In the future, we will hopefully be able to move beyond these blunt measures and better assess genetic risk. Such understanding would allow us to better target screening to those at highest risk. This would prevent unnecessary testing in low-risk adults and promote screening in people at truly increased risk. Already in diabetes researchers have identified specific genetic variants that predispose people to diabetes; in oncology, BRCA1 and BRCA2 are already being used in the clinics to identify women at very high risk of breast and ovarian cancers.
Our environment also contributes to our risk of colon cancer. Population studies have demonstrated that as people immigrate from Japan to the United States their risk of colon cancer increases. Such “natural experiments” provide strong evidence that something about our Western way of life predisposes us to colon cancer, but the exact reasons are still unclear. Though some have suggested that high fat, low fiber diets may play a role, these data have not established causality. Contrast this degree of understanding with cervical or lung cancer. In cervical cancer we have established that the cause of the disease is infection with the human papillomavirus or HPV; this understanding has led to the development of the first vaccine against cancer. Likewise, while it is easy to take for granted today, the knowledge that smoking is the major risk factor for lung cancer has had enormous implications and saved countless lives. Hopefully one day we will learn more about the modifiable risk factors for colon cancer and be able to prevent it altogether.
Given these limitations, it’s remarkable to consider that our current state-of-art — routinely screening all Americans over age 50 with fecal occult blood testing, sigmoidoscopy or colonoscopy — is proven to reduce death from colon cancer by 33%. If we simply increased the proportion of Americans being screened today to 90%, we would prevent 19,000 deaths annually.3 Still, tragedies like the one in my family are a harsh reminder that while we have made much progress we have much farther to go.
- Shantanu Nundy, M.D.
1 http://www.ahrq.gov/clinic/uspstf08/colocancer/colosum.htm
2 http://caonline.amcancersoc.org/cgi/content/full/CA.2007.0018v1
3 http://www.prevent.org/content/view/50/120/