Breast Cancer

on Thursday, February 17, 2011

The British Medical Journal recently published a study that examined the data of nearly 2 million breast cancer screenings and found that of 2,000 women screened regularly for ten years, one will benefit and avoid dying from breast cancer, but ten healthy women will have needlessly undergone mastectomies, radiation and sometimes chemotherapy, and another 200 will have endured a false alarm and follow-up tests and biopsies.  Breast cancer screening looks like good example of the false positive paradox, where an accurate test can lead to mostly incorrect results. (A 99% accurate cancer test will give 99.02% wrong answers if 1 in 10,000 women have cancer)

Based on this study, we can determine that if a woman is diagnosed with breast cancer, the probability that she actually has cancer is between 0.5% and 9%. After the initial diagnosis indicating cancer, requiring further testing, the woman is likely to have cancer 1 in 200 times. If upon further testing it is determined that she actually does have cancer and treatment is needed (breast removal, radiation, chemotherapy), only 10% of women will actually have needed the treatment -- 90% of them have harmless lesions.

Unfortunately, doctors and information brochures do not accurately describe risks involved in receiving regular screenings, encouraging all women to have regular screenings. This is medically unethical, and allows insurance companies to raise insurance rates for women who are diagnosed with cancer, even though 90% of them never actually had cancer.

Pamphlets inform women that screening either leads to less invasive surgery or simpler treatment, although it actually results in more surgery, more mastectomies, and more use of radiotherapy because of overdiagnosis. Pain caused by the procedure is sometimes mentioned, although it is probably the least serious harm, as it is temporary. Additionally, none of the information indicates that the tests are wrong over 90% of the time.

"A survey of American and European women found that 68% believed screening reduced their risk of contracting breast cancer, 62% that screening at least halved mortality, and 75% that 10 years of screening saved 10 of 1000 participants (an overestimate of 20 times). Another study showed that only 8% were aware that participation can harm healthy women and that 15% believed their lifetime risk of contracting the disease was more than 50% (an overestimate of five times).

Breast Cancer Rates
The vast majority of women around the world have never heard what the medical evidence supports. In fact, it’s so opposite to what we continually hear, that it can even sound incredible.

Yet, this is just one cancer screening test.

Think of the far greater interests advocating other preventive health interventions, such as surrounding obesity, heart disease, cancer, health indices and “healthy” eating. This study serves as a valuable example and reminder that, all too often, health information is more marketing and disease mongering than we may realize."

A pamphlet with information based on objective interpretation of the available studies has been created. It is quite informative and I'd recommend reading it.