Friday, August 24, 2012

Mammograms In Young Women

I'm back in the US now most of the time, and this blog has been fairly inactive. I don't have exciting stories from Uganda or South Sudan to write about (for the time being...stay tuned). So I thought I would try something new.

Many of my friends and patients have really good questions about health issues, and often turn to me because I'm just a Facebook message away, and it's hard to make a doctor's appointment just to ask a couple of questions. I'm going to start answering some of them here, because a lot of people have similar questions.

So today's question is:
I'm under 40 and I'm worried about breast cancer. Why can't I get a mammogram?

Mammograms are basically x-ray images of the breast. We use them to detect breast cancer in women who have no symptoms of cancer.

It's important to understand the difference between a screening test and a diagnostic test. A screening test is done in asymptomatic people who are at risk for a particular disease. A diagnostic test is done in someone with symptoms of a particular disease, to find out what is causing the symptom. Most mammograms are screening tests. Once a woman has already felt a mass in her breast, she no longer needs a screening mammogram; she needs a diagnostic mammogram.

For a screening test to be useful, several things have to be true:
(1) It has to be able to detect the disease reliably in people who have it
(2) It shouldn't over-detect disease in people who don't have it
(3) The disease has to be treatable
(4) The outcomes of the disease should be improved by the screening test

Therefore, mammograms are only useful if they detect cancer early, and if treating the cancer that was detected actually prevents women from dying of breast cancer.

An example of a good screening test is the pap smear. It detects early disease (cervical dysplasia) very well, before it leads to cancer, and when you catch the early disease, you can treat it and prevent it from becoming cancer.
Other tests that we use for screening include the colonoscopy, the prostate-specific antigen (PSA, controversial), HIV testing, STD testing, blood pressure and cholesterol testing. Even a physical exam can be a screening test, such as a listening to the heart rhythm, palpating the thyroid, or examining the breasts for masses.

So why don't women of all ages get mammograms? We've all heard of someone somewhere who died of breast cancer in her 30s, so wouldn't you want to prevent it?
First, mammograms aren't very effective in young women. Women under 40 have very dense breast tissue, and the mammogram imaging can't see through the tissue to detect the signs of cancer.
Second, breast cancer in women under 40 is extremely rare. Even though we've all heard of a case or two, those are the outliers. Breast cancer is largely a disease of age. Only a very small percentage of breast cancers are inherited, so the absence a family history of breast cancer is not protective.
Third, it's not clear that screening would help women who get breast cancer at a young age. Those women often have aggressive forms of cancer, which progress despite treatment. While early detection has helped some women catch their cancer early and successfully treat it, other women whose cancers were caught by mammogram early still went on to die of the cancer. This is because not all cancer is the same. Some breast cancers are slower growing, while others are fast and metastasize quickly. If the mammogram catches the cancer but the woman still dies of it despite treatment, then the mammogram didn't help.

Should anyone be screened at a young age?
Yes, some people should. People with a strong family history (for example, two first-degree relatives with breast or ovarian cancer at young ages) should talk to their doctor about being tested for genetic syndromes such as BRCA. They may be candidates for early screening because of their risk profile. However, most people with average risk do not benefit from early screening.

Is cost an issue?
Yes, it is. Cost is not the only reason not to do screening tests, but it is important to consider.  If we were to run every test available on every person all the time, we would be out of money in a heartbeat. However, the fact that something costs money isn't a reason not to do it. Cost-effectiveness studies look at how much a particular screening strategy costs - how much money is spent to detect one case, or to save one life? It can also be evaluated in terms of effectiveness - how many people need to be screened to detect one case?
However, with mammograms, cost is not really the issue preventing screening in young women. Mammograms are relatively inexpensive, but because they are largely ineffective in young women, the costs of doing them would be money wasted - money that could be better spent on other things, like researching treatments for breast cancer.

For more information here is a good fact sheet from the National Cancer Institute about mammograms.

1 comment:

rachel said...

fantastic as always, and extremely informative. thank you, veronica.