November 2, 2006

Breast Cancer and OC: What’s the Link?

According to a new meta-study published in the October issue of Mayo Clinic Proceedings, oral contraceptives may increase the risk of breast cancer in pre-menopausal women, particularly for women who have not had any children.

Well that’s not good news. But before you check the expiration of the condoms in the bottom drawer, there are other things about this study that you should take into account.

Ian at RHRealityCheck.org, a blog on reproductive health, raises some excellent questions about both the study’s conclusions (which some right-wing media outlets are only too happy to twist and repeat) and the authors behind it.

He first notes that the report’s lead author, Dr. Chris Kahlenborn, is affiliated with The Polycarp Research Institute. TPRI’s website includes this statement:

“TPRI will support research efforts that improve the spiritual condition of men and women, and will not promote methods or intentions that are inconsistent with the ethical and moral guidelines of the Catholic Church…”

Ian continues:

For the purposes of the Mayo article, Dr. Kahlenborn lists his email as drchris@polycarp.org, and his mailing address as “Department of Internal Medicine, PO Box 263, Hollidaysburg, PA.” Seem strange to you that a doctor associated with a “Department of Internal Medicine” would prefer his email at his nonprofit instead of at his hospital or medical school? Well, one reason here might be that there is no hospital in Hollidaysburg, PA. Another might be that that mailing address is actually the EXACT SAME address that TPRI lists on its website. From the looks of it, Dr. Kahlenborn just felt like being associated with a “Dept. of Internal Medicine,” so he made one up.

Another co-author, Dr. Francesmary Modugno, was a computer science specialist (that’s actually her PHD), who got a Master’s in Public Health in 1998 and has since fervently devoted her research to trying to establish a link between contraceptives and breast cancer.

The study’s other two authors apparently don’t wield political axes. But there’s a lot to consider here. OBOS is going to be talking to its experts about this study and may have more to say on the topic soon.

So how do we deal with this information in the short term? Let’s look at an editorial by Dr. James R. Cerhan published in the same issue of Mayo Clinic Proceedings. After asking the question, “How should clinicians counsel their patients at this time?” Cerhan delivers some noteworthy guidance:

First, OCs are extremely effective in preventing pregnancy when used correctly. Second, although OCs appear to be carcinogenic, the relative risk is small, and the absolute risk (excess breast cancers due to OC exposure) is very small. For example, the Oxford pooled analysis estimates that the excess number of cases of breast cancer expected to be diagnosed up to 10 years after discontinuation of OC use among 10,000 European or North American women is 0.5 cases for OC use from age 16 to 19 years, 1.5 cases for OC use from age 20 to 24 years, and 4.7 cases for OC use from 25 to 29 years. These cases are also likely to be clinically localized.

Third, although a formal risk-benefit analysis is beyond the scope of this editorial, all risks and benefits of OC use must be considered, not just the risk of breast cancer. Other cancer risks may include cervical cancer and liver cancer in populations at low risk for hepatitis B viral infection.

Additionally, IARC has determined that there is convincing evidence that OCs decrease the risk of ovarian and endometrial cancer, and there is accumulating evidence that they may lower the risk of colorectal cancer. Other major noncancer risks of OC use include ischemic stroke, venous thromboembolism, and myocardial infarction, but because these are rare events in women of childbearing age, the attributable risks are very small.

Finally, there is a growing number of noncontraceptive health benefits associated with OCs, including relief from menstrual disorders; reduced risk of pelvic inflammatory disease, benign breast disease, uterine leiomyomas, and ovarian cysts; and improved bone mineral density.


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