Wednesday, February 12, 2014

Earlier isn't necessarily better

Well, everyone’s up in arms again about mammography and whether it is effective or not. Today’s culprit is an article in the British Medical Journal that analyzed a large Canadian study and found that mammography led to no reduction in mortality from breast cancer. Some are vehemently arguing that this study is flawed. But, this study builds on other studies that have had similar findings. I’m not ready to dismiss it yet.

Even though it goes against the common refrain, when it comes to breast cancer, early detection doesn’t necessarily mean better outcomes.

I know, for years we’ve been told: “Get a mammogram, catch it early, get treated, and you’ll be fine." But that is not always the case.

The reality is that some breast cancers are very aggressive, and even if they are discovered early and treated, will eventually metastasize and lead to death.

Other breast cancers are not aggressive, and will not spread and cause harm, even if left untreated or if they are treated later on. And some breast cancers may even go away on their own.

The problem is, right now we don’t know how to determine if a particular breast cancer is going to be aggressive or non-aggressive. We have clues, but we don’t know for sure. So we have to treat every breast cancer as if it’s the aggressive kind.

That is what leads to overtreatment.

Another problem is that, for an individual, this information is not helpful. If your doctor finds a tumor in your breast, what woman is going to say: okay, I’ll wait a while and see if it’s an aggressive or non-aggressive tumor? That kind of decision could cost a woman her life. On the other hand, submitting to unnecessary treatment can cause all kinds of side effects and medical issues that might be completely, well, unnecessary.

Here’s another way of looking at the issue of whether “catching it early” is really important. Let’s say there are two women, Jennifer and Sandra. Jennifer finds out about her breast cancer from a mammogram when she is 50. She is treated with surgery, radiation, and chemotherapy, and does well for a while. However, in spite of all the treatment, her cancer metastasizes when she is 55, and she dies at age 57. So you could say that after her cancer was discovered, Jennifer survived for 7 years.

Sandra finds out about her breast cancer when she is 55, when it is Stage IV and has already metastasized. Sandra dies at age 57. So you could say Sandra only survived 2 years after diagnosis. Both women die at the same age from a similar cancer, but Jennifer’s tumor was discovered earlier and treated, although this treatment didn’t extend her life.

This is called lead time bias. The National Cancer Institute puts it this way: “This increase in survival time makes it seem as though screened patients are living longer when that may not be happening... It could be that the only reason the survival time appears to be longer is that the date of diagnosis is earlier for the screened patients. But the screened patients may die at the same time they would have without the screening test.“  

So where does this leave us? Well, Dr. Deanna Attai, a breast surgeon in Burbank, CA had this to say on her Facebook page: “We need better tools - currently mammograms are a bit "one size fits none.” She continues: “Hopefully studies like these will promote more research. We need to identify who will actually benefit from mammography, and we predict which patients do not need screening. We are definitely moving towards more personalized care - we're just not there yet.”

Some links:
Too Many Mammograms
Overdiagnosis and Overtreatment of Breast Cancer

1 comment:

QueenTimely said...

Very enlightening post, Adena. It's important to tease out these issues and there's so much information out there. Thanks for your attention to it.