Colon Cancer Screening guidelines: How Have They Evolved & What Should You Know?

Ramesh Hariharan Aug 22, 2024

While reported incidence rates are lower, just ~80,000 new cases annually, all Indian cancer registries indicate a rising trend

Colorectal Cancer (CRC) is the third most commonly diagnosed cancer worldwide, with more than 1.93 million new cases in 2020, and predicted to reach 3.2m by 2040. It is also the second leading cause of cancer deaths, causing 0.94m deaths in 2020.

The CRC picture in India is mixed. While reported incidence rates are lower, just ~80,000 new cases annually, all Indian cancer registries indicate a rising trend. Studies show that the mean age of diagnosis is as low as 47.2, with ~32 per cent below age 40, and most cases are diagnosed at later stages (3.8 per cent Stage I, 16.7 per cent Stage II, 50.7 per cent Stage III, 28.8 per cent Stage IV).

Fortunately, CRC is curable to a substantial extent when caught early. The cure fraction (the proportion of diagnosed CRC patients who survive past their acute cancer to the point of attaining roughly the same risk of death as the age- and sex-matched general population) is 62 per cent, 61 per cent and 58 per cent when diagnosed at stages I, II, III, respectively, but only 7 per cent when diagnosed at stage IV. We don’t have cure fractions specifically for India, but we know that in contrast to the above, only 40 per cent of CRC patients survive for 5 years from the time of diagnosis; this 5-year survival figure is one of the lowest in the world. Together, the above facts underscore the importance of screening for colorectal cancer in India.

According to US medical standards, or NCCN guidelines, a screening colonoscopy should be performed at age 50 for a few years, and then every five to ten years after that, up until age 75. A screening colonoscopy involves using a flexible tube equipped with a camera to examine the inside of the patient's colon, rectum, and anus. Usually, a specialist in gastrointestinal disorders does it. A low-fiber diet should be followed for two or three days prior to the colonoscopy, then on the last day, a clear liquid diet should be consumed. The night before the procedure, a laxative formula should be used to clear the colon. The 30 to 60-minute treatment is carried out under conscious sedation or general anaesthesia. During the procedure, any odd growths (polyps) are removed; if the growth is suspected, a second biopsy is carried out to confirm the cancer.

In the 1980s, colonoscopy-based colorectal cancer screening programs were implemented in the United States. Since then, the incidence of colorectal cancer has decreased by 40 per cent overall, although it has increased among persons under 50. Recent guidelines have addressed this by lowering the age of the first colonoscopy from 50 to 45 and even lowering yet to 40 in cases where a first-degree relative has colorectal cancer.

Colonoscopies need trained specialists, and the process is cumbersome, which reduces guideline adherence. Further, roughly 1 in 1000 cases could result in a colonic perforation requiring surgery, with the risk in the elderly being even higher (the NCCN guidelines therefore recommend discretion after the age of 75, and do not suggest a colonoscopy after 85). This has led to the development of non-invasive screening tests to select who should get a colonoscopy.

Stool-based tests provide a non-invasive option; one just takes a sample of one’s stool and sends it to a laboratory where suitable tests look for traces of blood as an indication of CRC. Many variants of this test exist, two of the most notable being (G)-FOBT and FIT. Both have sensitivities of only 50 per cent-66 per cent for stages I, II and III, but the latter has a substantially better specificity at 90 per cent compared to the former’s 78 per cent. While cheap, their performance is not adequate. More sophisticated multitarget DNA tests, e.g., the Exact Sciences’ stool-based Cologuard test (sensitivity of 94 per cent and a specificity of 87 per cent), improve upon this and are recommended by the NCCN guidelines every 3 years, with any positives being confirmed by a colonoscopy.

Stool-based tests too are known to have adherence issues, given the need to handle stool. This has led to much research effort on non-invasive blood-based tests. Several publications now show a sensitivity of ~65 per cent for Stage I, and >80 per cent for stage II, III and IV, with specificity of ~90 per cent. These include studies on Indian subjects by Strand Life Sciences and on US subjects by Guardant. It is perhaps a matter of time before these blood-based tests too enter the guidelines, with any positives being confirmed by a colonoscopy.

In essence, for the average person wanting to detect CRC early, the screening protocol suggested by the NCCN guidelines would then be a colonoscopy at 45, a stool- or blood-based test every 1-3 years and a colonoscopy every 5-10 years thereafter.

The author is the CEO of Strand Life Sciences