Last year, Chien Hua Chen, Chi Pang Wen, and Min Kuang Tsai published their findings on the relationships between FIT value and cancer risk in their study “Fecal immunochemical test for colorectal cancer from a prospective cohort with 513,283 individuals”. Unique to their study was the analysis of how age affected risk. Using a massive pool of subjects, the researchers had 513,283 Taiwanese adults participate in FIT screening between 1994 and 2007, and progressively analyzed the data for the next decade.

FIT (Fecal Immunochemical Test) is currently the most popular blood test for colorectal screening. It tests for hidden blood in the stool, which is one of the earliest signs of colorectal cancer. The cutoff value for a recommended colonoscopy following the FIT test is 100ng/mL (nanograms per milliliter), which means those with a test result of 100ng/mL or higher have enough blood in their stool to make doctors suspicious of colorectal cancer. However, colonoscopies are uncomfortable, expensive and include a small risk of a perforated colon. Understanding whether a patient should undergo a colonoscopy based on their FIT value is crucial. To elaborate, if the FIT result suggests the patient is healthy, then the patient can avoid paying for the costly and potentially dangerous procedure. If more people get a colonoscopy only when necessary then that will also lower our nation’s healthcare expense. Making that judgement requires one to know what their FIT value actually means and how it relates to colorectal cancer risk.

Three main correlations the study discovered between FIT value and colorectal cancer. First, in each age group, the higher the FIT value, the higher the cancer risk. As evident in Graph 1, compared to individuals with FIT values less than 100?ng/mL, the risk increased nearly 400% at FIT values of 100-199, 800% at FIT values of 200-299, and 2300% at 800-999?ng/mL.

Graph 1

That being said, although a higher FIT value is associated with a higher risk, the younger participants had a much lower risk compared to older participants even with the same FIT value. Graph 1 explicitly illustrates how risk factor differs between ages (each line indicating a different age group). Using  NNS as a means to measure risk and prevalence of colorectal cancer among different age groups, the researchers found NNS was smaller for older age groups and much larger for younger age groups. For instance, Graph 2 shows that NNS for age 60-69, 50-59, 40-49, and 20-39 for a FIT value less than 100ng/mL was 10, 18, 42, and 156, respectively. Furthermore, at a FIT value of 500?ng/mL, NNS for ages 20 to 39 years was 169, a 10-fold increase compared to NNS for ages 50 to 59 years, which was 16.

Graph 2

The third relationship made was based on cancer latency. In each age group, the larger the FIT value, the faster the manifestation of the cancer. To elaborate, while the average latency for a FIT value less than 100ng/mL was 6.6 years, the average latency for 600 to 799ng/mL was only 3.9 years. Graph 3 demonstrates this correlation, showing a linear relationship between cancer latency and FIT values. According to this relationship, cancer developed about a year sooner for each additional 200ng/mL rise in FIT value.

Graph 3

Each age group has a different average cancer risk. Using a single cutpoint value doesn’t take age into consideration. A major flaw in modern healthcare is our use of such expensive procedures, such as the colonoscopy, when it is unnecessary. While it is important to have people with symptoms of or a family history of colon cancer, that rule does not apply to everyone. The data collected heavily supports the belief that incorporating one cutpoint value overestimates the cancer risk for those with FIT values less than 400ng/mL. Even for those who are concerned about developing colorectal cancer despite having a high NNS or low cancer risk (according to the data for their specific age group), the third relationship between FIT value and cancer latency shows that it takes about 4 to 6 years for someone initially having a FIT value of less than 100ng/mL to reach the value of 700ng/mL that is associated with the manifestation of colorectal cancer. FIT had a sensitivity performance of 93%, meaning only 7% of FIT results were false negatives. This number decreases significantly with continuous use of FIT. Therefore, taking the FIT tests annually almost guarantees detecting the cancer before it develops. 

The study suggests a significant policy change for some organizations providing screening programs. As of now, unless a better and more inexpensive screening method becomes available on the market, FIT testing should be used as the “first line of defense” screening option, before a colonoscopy. In addition, doctors should become more aware of the various cancer risks among different age groups, and use their understanding of these differences to help their patients follow the most appropriate next-step in preventing or treating colorectal cancer.