Monday, March 8, 2010

The Lottery

I was told by a friend that the statistics of screening mammography are too confusing for people to possibly understand so clinicians need to continue to make recommendations.  I mean it's ok to talk about the greater likelihood of antibiotics making someone sicker with a viral infection than speeding up their recovery.  10 years ago that was a discussion that would have taken a great deal of time.  Nowadays a child has a cold and parents generally would have to be convinced to give the kid antibiotics.  They accept the fact that the odds of harm outweigh the chance of benefit.  They know there's a problem with antibiotic resistance and some know the harms from allergic reactions and colon infections that antibiotics cause not infrequently.  

And then we were talking about the lottery last evening at sunset on the bikes and it hit me,  screening mammograms are like slot machines.  

We have 30 years of experience and now we can tell you the odds of winning or breaking even or losing at the screening mammogram machine.  

So picture the big expensive slot machine that is screening mammography in your head right now.  40 year old women pay some money and go pull the lever and there's 2 possible results displayed on the screen positive or negative.  If it's negative,  she leaves and returns next year to pay and play again.   Most women get a negative result.

Now if it's positive,  there's another machine next to the 1st and it has a lever that's pulled and the screen can say negative or positive.  (this is the follow up mammogram or ultrasound because of a concerning screening finding).  And most of the time this is negative. 

This is as far as most women get playing the screening mammogram game.  They break even.  The second group has a good degree of anxiety and fear between pull one and two but no harm done (except for the radiation exposure but that's another story)

Now some women get a positive result on the 2nd pull and have to go on to a biopsy which can be negative or positive;  if it's positive that means they found cancer.  It's treated and hopefully it's cured.  

Well those women who get this far,  have cancer found and are ultimately cured because it was caught by the mammogram early,  they won.  Screening mammography saved their lives.  The chance this will happen is 1 in 2000 over 10 years for women age 40.  This represents 15% of all the women destined to die of breast cancer over those 10 years.  Screening mammograms won't save the other 85%  (better treatments for cancer and not handing out hormone replacement therapy after menopause saves another 15%)  

The big problem is that the slot machine also tells some women after going through the 3 rounds of tests,  getting diagnosed and treated for cancer that it saved them also.  But there are 10 women for every 1 really saved by the test who were diagnosed and treated for a cancer destined never to cause symptoms in their life.  These women are the ones who lost at the slot machine.  It harmed them with the unnecessary label of "breast cancer survivor".   It's impossible to know on an individual basis who really won the game and who was harmed.  Which is pretty damn infuriating to me.  What we do know is the ratio of 10 to 1.  10 harmed with an unnecessary diagnosis for every one saved.  

So when you chose to participate you have a 1 in 2000 chance of being saved and a 10 in 2000 chance of being harmed.  

There's another group that goes through all this mess and gets diagnosed earlier with cancer but it doesn't affect their survival either way.  They are going to survive the cancer or not regardless of whether it's caught a year or 3 earlier.  You could argue that they are harmed by the machine stealing a sizable chunk of what feels like cancer free living.  We know the odds of being one of those folks,  it's also 10 in 2000 over 10 years.  

I don't know,  maybe it is confusing.  

I need to make a video with animation and pie charts and such.  

Anything to make the decision to participate completely understood.  It's important since the same analysis of benefits/harms can guide most medical decisions.  Which keeps the individual in charge and empowered;  Perhaps even immune to the tricks of marketing.  

How much less expensive and less harmful do you think health care would be with people thus immunized?