Blood Test Shows Potential in Detecting Colorectal Cancer, Offers Screening Option With 83% Accuracy

Colorectal cancer is the third most common cancer in the world, accounting for almost 10% of all global cancer cases. It has been shown that some screening tests may help find colorectal cancer at an early stage and may also decrease the cases of deaths from this disease.

Despite the available technologies, screening for colorectal cancer has a reputation for being difficult. In fact, some screening tests may pose some harm. A new clinical trial, however, suggests that detecting this disease may be as easy as a simple blood test in the future.

Importance of Colorectal Cancer Screening

In the US, over 150,000 people are diagnosed with colorectal cancer annually, with more than 50,000 dying each year. Experts believe that early detection at the precancerous stage is an important factor in preventing the disease.

It typically affects older adults, beginning as small clumps of cells known as polyps which form inside the colon. Although polyps are not cancerous in general, they can potentially turn into cancer over time. They typically don't show any symptoms, and it is the reason why regular screening tests for locating and removing polyps are needed to prevent the illness.

The American Cancer Society recommends screening for colorectal cancer starting at age 45. However, only less than 60% of those who are eligible are up to date on their screening tests. If every qualified person gets screened regularly, almost 90% of deaths related to colorectal cancer may be avoided.

Highly Accurate Screening Test

A new study, published on March 14, reported the promising result of the novel screening method called Shield. It is a cell-free DNA blood-based test (cfDNA) funded by Guardant Health.

The clinical trial was conducted on 7,861 participants from the US, who had both a colonoscopy and a blood test. The blood test detects circulating tumor DNA shed into the bloodstream from the tumors.

It was revealed that the new test detected colorectal cancer at early, treatable stages 83% of the time with high accuracy. For the 10% of patients whose colonoscopy test found nothing, the blood test falsely diagnosed colorectal cancer. Meanwhile, the test was less successful at spotting advanced precancerous lesions, with only 13% being detected. In comparison, colonoscopies are about 93% successful at early detection, and fecal tests are up to 42% accurate.

The new screening test has not been currently approved by the Food and Drug Administration (FDA), although Guardant Health hopes that a decision will be made later this year. If it gets approved by the agency, the blood test will be administered every three years, beginning at age 45. For comparison, current screening guidelines recommend a colonoscopy every 10 years for people at average risk, while fecal testing is required every year.

The researchers clarified that Shield is not intended to replace a colonoscopy. Individuals with symptoms and risk factors for colorectal cancer, including family history of the disease, are still required to undergo a colonoscopy.

The researchers noted that the results of their study are a promising step toward developing more convenient ways to detect colorectal cancer at an early stage where it is more easy to treat. They also claim that the novel blood test offers an alternative for individuals who may decline conventional screening options.