CANCER SCREENING. Specifically ovarian

No, she is not disguised as a unicorn, she is posing in front of an obelisk raised by the woman Pharaoh, Hatshepsut  

Karnak temple, 2008

 

It is only 2:30 and already this day has begun to qualify as the most boring, least productive, most  exceptionally tedious day of my life.  I am waiting, reluctantly, to answer the door when – and maybe if – the FedEx man arrives to deliver my new iPad.  He has tried twice and I haven’t been home.  If I don’t answer the door today the machine will go back to Apple, somewhere in the Cloud, and I will be doomed to many long telephone adventures – of the sort I hate very much.  Not only that: my stupid left knee has kept me from walking more than about 50 ft. at a time, precluding any useful activity outdoors.  If you think I am complaining too much over too little, you’re probably right, but I don’t care.  I am in a foul mood.

Well, one thing I can do is write a blog.  You may have seen this somewhere: it has been on the CBS and NBC evening news, Yahoo, and the NYTimes.  It appears that scientists at MD Anderson Cancer Center at the University of Texas have just released a announcement concerning the results of a clinical trial that have been conducting for ten years.  It seems that they have been measuring the level of the protein CA125 in the blood of healthy women yearly, then referring them to ultrasound if there is a marked increase. Medical science has known for years that CA125 is “up-regulated” in women with ovarian cancer.  The normal level of this blood marker in healthy (non-cancerous) women is 35 or less: I don’t know what the units are, and in my present state of mind I don’t care.  This has tempted the aforesaid medical science to use CA125 as an early warning signal, but this is discouraged by the authorities.  The problem is that things other than OVCA can affect CA125, and there is great variability between women.   

What the Texas group did was to monitor changes in CA125, and refer anyone with a marked jump for ultrasound.  They claim this has high “specificity”   This means that if you test negative, you probably are negative (don’t have OVCA).  They are rather more cagey about “sensitivity” – the probability that, if you have the disease, the test will catch it.  As with so many of these announcements we are cautioned that the test is not ready for prime time.

I don’t know what to think of this news.  In an important way, MD Andersen is poaching on the territory my group also occupies.  (Actually, of course, I don’t give a tinkers damn who develops a useful test, so long as one is developed.)  My Fred Hutch group also is using changes in CA125, together with changes in another protein called HD4, to select women for ultrasound.  We, however, are far more fancy.  We use something called a “parametric empirical Bayesian longitudinal algorithm” to select our “positives”.  If you are like me you know what each of those words (except perhaps "Bayesian”) means individually, but have no notion of what they mean all strung together.  Well, Bayes was a statistician who worked on conditional probability, I think it’s called.  He developed a method to re-compute probability in the light of accumulating evidence.  A childish example:  You have 10 M&Ms, and you are blind.  One is red, the others are black.  You are deathly allergic to red M&Ms, but you are very hungry.  Before you pick out one and eat it, the probability of getting the red one is 1/10, or 0.1.  Say you eat one and don’t die – but are still hungry.   If you dip into the bowl again, the probability of getting the deadly M&M now is 1/9, or 0.11.  If you still don’t die the revised probability of death by M&M is 1/8.  And so forth. 

So that, more or less, is the way that my groups plans to use repeat measurements of CA125 (and HD4).  It should work.  My greatest fear, though, is that it will reliably detect OVCA only after it is too late to do much about it.

The FedEx man has arrived!                                                                               

You can read the article yourself at http://news.yahoo.com/ovarian-cancer-screening-test-seems-promising-142618079.html