Estrogen exposure helps protect against colorectal cancer (CRC), and in some instances, the protection is site specific, a new analysis finds.
In a 17-year study involving almost 5,000 women, researchers from Germany found that hormone replacement therapy, oral contraceptive use, pregnancy, breastfeeding, and menopause at age 50 or older were all significantly associated with reductions in CRC risk.
Interestingly, the reduced risk of CRC observed for pregnancy and breastfeeding only applied to proximal colon cancer, while the association with oral contraceptive use was confined to the distal colon and rectum.
The results were published online in JNCI Cancer Spectrum.
CRC is the second most common cause of cancer death. It is responsible for more than one million deaths globally, according to the latest figures from the Global Burden of Disease 2019 Cancer Collaboration.
And sex seems to make a difference. The Global Burden analysis, echoing previous data, found that CRC is less common among women and that fewer women die from the disease.
Little, however, is known about the mechanisms of estrogen signaling in CRC or the impact of reproductive factors on CRC, despite a large amount of literature linking CRC risk to exogenous estrogens, such as hormone replacement therapy and oral contraceptives.
In the current analysis, the team recruited 2,650 patients with CRC from 20 German cancer centers between 2003 and 2020. Researchers used standardized questionnaires to garner the women’s reproductive histories.
A matched control group of 2,175 participants who did not have a history of CRC was randomly selected from population registries. All analyses were adjusted for known CRC risk factors, such as age; body mass index; education level; family history; having previously undergone large-bowel endoscopy; diabetes; and smoking status.
The researchers found that each pregnancy was associated with a small but significant 9% reduction in CRC risk (odds ratio, 0.91), specifically in the proximal colon (OR, 0.86).
Overall, breastfeeding for a year or longer was associated with a significantly lower CRC risk, compared with never breastfeeding (OR, 0.74), but the results were only significant for the proximal colon (OR, 0.58).
Oral contraceptive use for 9 years or longer was associated with a lower CRC risk (OR, 0.75) but was only significant for the distal colon (OR, 0.63). Hormone replacement therapy was associated with a lower risk of CRC irrespective of tumor location (OR, 0.76). And using both was linked to a 42% CRC risk reduction (OR, 0.58).
Although age at menarche was not associated with CRC risk, menopause at age 50 or older was associated with a significant 17% lower risk of CRC.
In an email interview, lead author Tobias Niedermaier, PhD, expressed surprise at two of the findings. The first was the small association between pregnancies and CRC risk, “despite the strong increase in estrogen levels during pregnancy,” he said. He speculated that pregnancy-related increases in insulin levels may have “largely offset the protection effects of estrogen exposure during pregnancy.”
The second surprise was that the age at menarche did not have a bearing on CRC risk, which could be because “exposure to estrogen levels in younger ages [is] less relevant with respect to CRC risk, because CRC typically develops at comparably old age.”
John Marshall, MD, who was not involved in the research, commented that such studies “put a lot of pressure on people to perform in a certain way to modify their personal risk of something.” However, “we would not recommend people alter their life choices for reproduction for this,” said Dr. Marshall, chief of the Division of Hematology/Oncology at Georgetown University, Washington, D.C.
Dr. Niedermaier agreed that “while this knowledge will certainly not change a woman’s decision on family planning,” he noted that the findings “could influence current CRC screening strategies, for example, by risk-adapted screening intervals [and] start and stop ages of screening.”
Dr. Niedermaier and colleagues’ work was funded by the German Research Council, the German Federal Ministry of Education and Research, and the Interdisciplinary Research Program of the National Center for Tumor Diseases. Dr. Niedermaier has disclosed no relevant financial relationships. Dr. Marshall writes a column that appears regularly on Medscape: Marshall on Oncology. He has served as speaker or member of a speakers’ bureau for Genentech, Amgen, Bayer, Celgene Corporation, and Caris Life Sciences.
A version of this article first appeared on Medscape.com.