Lower colorectal cancer mortality after removal of low-risk adenomas

1. Removal of low-risk adenomas was associated with lower mortality from colorectal cancer. 

2. Removal of high-risk adenomas was associated with higher mortality from colorectal cancer. 

Evidence Rating Level: 1 (Excellent)

Study Rundown: Most colon cancers arise from growths called adenomas. The goal of colorectal cancer screening programs is to reduce colon cancer mortality by identifying and removing these growths before they become cancerous. However, few large, high-quality studies have looked at the risk of death due to colon cancer after adenoma removal.

This study makes use of Norway’s national Cancer Registry, which includes information on almost all colorectal adenomas removed by Norwegian health care providers since 1993. Norwegian guidelines recommend screening every 5 years for people with multiple adenomas and every 10 years for people with high-risk adenomas. The authors found that people who had low-risk adenomas removed had a lower risk of death from colorectal cancer compared to the general population. On the other hand, people who had high-risk adenomas removed had a higher risk of death from colorectal cancer compared to the general population. Overall, people who had any adenoma removed had the same risk of death from colorectal cancer as the general population.

The increased risk of death among those with high-risk adenomas may reflect a predisposition towards more aggressive cancer in these patients, or a failure at initial polypectomy to remove all the pre-cancerous tissue. It is not clear from this study whether increased intensity of surveillance in these patients would have reduced their risk of death. The lower risk of death among those with low-risk adenomas removed suggests that these people may not need further surveillance.

Click to read the study in NEJM

Click to read the accompanying editorial in NEJM

Relevant Reading: Long-term mortality after screening for colorectal cancer

In-Depth: Data from over 40,000 patients followed over a median of 7.7 years was used in this study. The Cancer Registry did not include information about polyp size and the exact number of polyps. Thus, the high and low-risk categories were based mostly on pathology, whereas current guidelines would also take into account number and size of polyps. The authors reviewed a random sample of pathology reports from their study cohort to determine how accurate their risk classification method was; they found that about 30% of adenomas classified as low-risk in the study would have been classified as high-risk by current guidelines and 8% of adenomas classified as high-risk in the study would have been classified as low-risk by current guidelines. This suggests that the risk of death is probably over-estimated in the low-risk group.

The “expected”number of colorectal cancer deaths serve as the control in this study. This figure was based on colorectal cancer deaths among members of the general population who received a diagnosis of colon cancer during the study period. Presumably, this includes people who were referred for endoscopy and had a polyp removed (i.e. those in the Cancer Registry), people who were referred for endoscopy and did not have a polyp removed, and people who had no endoscopy prior to diagnosis.  It should be noted that Norway did not screen healthy individuals for colon cancer during the study period. All the individuals in the Cancer Registry were referred to endoscopy for specific clinical indications, not routine screening.

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