A new study determined if colorectal cancer screening reduced cancer incidence and mortality in women as effectively as in men.
Colorectal cancer is a leading cause of cancer deaths worldwide. In the United States, it is the second leading cause of cancer mortality and it is the most frequently occurring cancer in Europe. Colorectal cancer screening helps in the early detection of cancer and reduces cancer incidence and mortality. The commonly used screening methods include fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy.
Currently recommended guidelines for colorectal cancer screening
The current guidelines for colorectal cancer screening recommend fecal occult blood testing, sigmoidoscopy, or colonoscopy every 10 years for adults, starting at 50 years of age and continuing until 75 years of age. The screening is recommended to begin at 40 years of age in populations at higher risk. Colonoscopy as a screening method involves high cost, expertise, inconvenience and risk. Therefore, sigmoidoscopy and fecal occult blood test are the more commonly used methods.
The current recommendations for colorectal cancer screening do not take sex into consideration. Although men and women have similar risks of developing colorectal cancer during their lifetime, some studies show that women develop colorectal cancer at an equivalent level as men but it occurs almost a decade later in life compared to men.
The effectiveness of colorectal cancer screening is different in men and women
A recent research review published in the BMJ, discussed the effectiveness of colorectal cancer screening in women based on the results of a recent study that included 98,678 adults, 50-64 years of age, without a history of colorectal cancer. Of these participants, 20,552 were screened for colorectal cancer using flexible sigmoidoscopy and the remaining 78,126 did not undergo the screening. A part of the screening group of participants were screened only by sigmoidoscopy while others were screened by a combination of sigmoidoscopy and fecal occult blood testing. The mean follow-up period of the study was 14.8 years.
The results showed a 34% risk reduction in the incidence of colorectal cancer and a 37% reduction in colorectal cancer mortality in the screening group compared with the control group. However, combining fecal occult blood testing with sigmoidoscopy did not increase the efficiency of colorectal cancer screening.
Furthermore, the researchers observed an absolute risk reduction of 0.78% in colorectal cancer incidence and 0.33% in colorectal cancer mortality in men. Interestingly, the results showed a very little effect of colorectal cancer screening on the incidence or mortality in women.
Sigmoidoscopy is not an effective screening tool for women
While the adherence rate to the screening procedures was similar in men and women, the study results did not find a significant effect of colorectal screening on the incidence and mortality in women. After a follow-up of 10-17 years in previous randomized controlled trials, the researchers found that sigmoidoscopy reduced colorectal cancer incidence by 18-26% and colorectal cancer mortality by 22-31%. However, the same level of effectiveness of sigmoidoscopy was not observed in women.
Some researchers suggest that women develop peak levels of colorectal cancer almost a decade later in life as compared to men. This difference could explain the lower effectiveness of colorectal cancer screening in women. Based on current guidelines, the one-time screening of colorectal cancer in women may be too early in life and it may miss cancer that might develop later.
It may be significant to include sex in the colorectal cancer screening guidelines
The study results suggest that sex may be an independent factor in the detection of colorectal cancer. Some studies have found different rates of colorectal cancer detection in men and women. These findings suggest that a more effective diagnosis can be achieved if the screening guidelines are modified to include sex in addition to age and family history.
Moreover, this study concluded that sigmoidoscopy results are effective for a follow-up of 15 years. However, as per the current US guidelines, sigmoidoscopy screening should be repeated every 5 to 10 years. Researchers suggest that extending the screening intervals to 15 years may result in significant savings for the health departments.
Women may benefit from modifications in screening recommendations
In conclusion, the effectiveness of sigmoidoscopy for colorectal cancer screening in women is uncertain. The study results showed little effect of flexible sigmoidoscopy in reducing colorectal cancer incidence and mortality in women. The researchers suggest that these results may be helpful in designing future colorectal cancer screening recommendations that will prove to be as effective in women as in men.
Written by Preeti Paul, MS Biochemistry
Reference: Jacqui Wise. Women see no benefit from colorectal cancer screening, study finds. BMJ 2018;361;k1747 doi: 10.1136/bmj.k1747