In an effort to understand conflicting information about whether breast cancer makes colorectal cancer more likely, researchers at the University of Pennsylvania reviewed information from a large group of women with breast cancer and compared their rates of colorectal cancer to women without a history of breast cancer.
Using a research database from the United Kingdom that included 17,415 women with a history of breast cancer and 69,660 women without breast cancer, the research team calculated the risk for a subsequent colorectal cancer. The relative rate for colorectal cancer among those with breast cancer was 0.80.
The team concluded
Women with a prior diagnosis of breast cancer are not at an increased risk of colorectal cancer; these women can follow average risk screening guidelines for colorectal cancer.
Their results were reported in the [October 2005 issue of the *American Journal of Gastoenterology*](http://www.amjgastro.com/showContent.asp?DID=4&SessionGUID=B97EAA8F-8AE5-4F62-B825-A7AAC2731B33&id=ajg_316102005&type=abstract)
An [article in *The Lancet*](http://www.thelancet.com/journals/lancet/article/PIIS0140673600041970/abstract) in 2001 found a slightly reduced risk for colon and rectal cancer after breast cancer, compared to what was expected in the overall population. Women with breast cancer were 5% less likely to develop colon cancer and 13% less likely to be diagnosed with rectal cancer. Reduced risk was greatest in women whose breast cancer was diagnosed over age 65, in white women, and in women with local stage cancers.
Despite these results in the overall population a [2003 study](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12825849&query_hl=1) found that certain subgroups of breast cancer survivors had an increased risk to develop colorectal cancer. That included women with
+ a family history of breast cancer
+ high body mass index (BMI) over 30 mg/m²
+ lobular rather than ductal cancer
Most women with breast cancer probably can follow colorectal screening guidelines for people of average risk but should discuss their individual risk factors with their doctors.