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Breast Cancer Does Not Increase Risk of Colorectal Cancer (dateline March 21, 2001)

A large study finds that having breast cancer does not increase the risk of developing colorectal cancer (cancer of the colon or rectum) later in life. The researchers hope that these results will help clear up confusion from previous studies, in which some data suggested a link between breast and colorectal cancer risk. In fact, according to the new study, women with a history of breast cancer may actually have a lower risk of developing colorectal cancer than the general population. Breast cancer patients and survivors should still be aware that colorectal cancer is the third leading cause of cancer-related deaths and should receive regular colorectal screenings beginning at age 50. However, having a history of breast cancer alone does not require women or their physicians to take additional measures to prevent colorectal cancer.

To conduct their study, Dr. Craig Newschaffer of Johns Hopkins School of Medicine and Public Health and his colleagues analyzed medical data from 227,000 women who had been diagnosed with breast cancer between 1974 and 1995. The information was obtained from the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) database. Overall, the researchers found that women with a previous breast cancer were 5% less likely to develop colon cancer and 13% less likely to develop rectal cancer than women in the general population.

Dr. Newschaffer and his colleagues are not sure why a history of breast cancer may reduce colorectal cancer risk and caution that the benefit is speculative at the moment. However, they suggest that having few children or using hormone replacement therapy (HRT) for a long period of time (more than five years) may provide protection against colorectal cancer. Long-term use of HRT and not having children until after age 30 (or never) can increase the risk of breast cancer.

Regardless of whether or not breast cancer provides protection against colorectal cancer, the researchers say that the most important information for breast cancer patients and survivors is that they are not at any additional risk for colorectal cancer compared to women who have not had breast cancer. Therefore, they do not need to take extra measures to prevent the colorectal cancer unless they as individuals carry a higher than average risk (for example, they have a strong family history of colorectal cancer, etc.). In the study, women over age 65, Caucasian (white) women, and those whose breast cancers were not metastatic (had not spread past the breast and lymph nodes) were at the least risk of colorectal cancer.

While a history of breast cancer does not increase the risk of colorectal cancer, the American Cancer Society reports that colorectal cancer is the third most common cancer in the United States (not including skin cancers). It is estimated that about 98,200 new cases of colon cancer (46,200 men and 52,000 women) and 37,200 new cases of rectal cancer (21,100 men and 16,100 women) will be diagnosed in 2001. Risk factors for colorectal cancer include advancing age, family or personal history of colorectal cancer, history of intestinal polyps or inflammatory bowel disease, high-fat diet (mainly from animal sources), physical inactivity, obesity, etc.

Similar to breast cancer, the chances of successful treatment and survival are the greatest when colorectal cancer is detected in early stages. Therefore, the American Cancer Society recommends that all people 50 years of age and older follow one of the following screening guidelines:

  • Yearly fecal occult blood test (FOBT)
  • Flexible sigmoidoscopy* every 5 years
  • Yearly fecal occult blood test plus flexible sigmoidoscopy every 5 years
  • Double contrast barium enema every 5 years
  • Colonoscopy** every 10 years

*a sigmoidoscopy involves examining the rectum and lower portion of the colon

**a colonoscopy involves examining the entire lining of the colon

In addition, women with a history of breast cancer are typically monitored by physicians for any signs of a recurrence or second cancer. This monitoring may include annual screening mammograms (for women who have not had mastectomies). Women should also receive regular physician-performed clinical breast exams and practice monthly breast self-exams.

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