Wednesday, December 31, 2008

Early Detection and Cancer Survival

The January issue of Wired magazine features a cover story about early cancer detection and its effect on survival rates. The article focuses on some detection methods, some of the difficulties in identifying real from false positives and one group in particular, The Canary Foundation, a research group whose focus is on developing early detection methods.

The article argues, based on cancer survival statistics, that "scientists should stop trying to cure cancer and start focusing on finding it early." The author notes that in the case of ovarian cancer, for example, discovery at stage I or II the 10-year survival rate is almost 90%, while the survival if diagnosis occurs later - at stage III or IV - drops dramatically to 20%. This makes sense. In early stages, before cancer has metastasized and spread, straightforward surgical intervention can remove most - if not all - of the cancer. Once it has spread, it is more difficult to treat and options are limited to more harsh chemo and radiation treatments.

The article, however, ignores another reality of the numbers it cites: early detection will improve survival rates even without any other intervention. The reason is the way cancer survival is reported. Typically survival is measured as relative 5-year survival, meaning the percentage of people still alive five years after diagnosis, compared with the general population. Early detection shifts the goalposts: the 5-year window now starts at an earlier stage. Even if these people have exactly the same progression as someone with a late-stage diagnosis, the survival rates will look much better.

Of course, we don't want to give up on early detection any more than improving treatment options. We do, on the other hand, want to understand what the numbers mean and how they're derived before we start changing policies or strategies based on them. Ideally with a combination of early detection and improved intervention we can start using intervals longer than 5 years as our standard measure of cancer survival.


4 comments:

Anonymous Coward said...

It was interesting to read about how many tumours you can detect early with improved imaging in an otherwise healthy individual. The problem is trying to identify which ones are a threat, which seems completely outside our knowledge....

Keith Robison said...

The previous comment is quite on target & will represent another inflation of the survival statistics with early detection -- many more of these patients have tumors that will never become lethal and hence do not represent 'cures'.

Since there are psychological and physiological (not to mention financial) costs to cancer treatment, early detection is not necessarily entirely benign.

Brooke said...

Detection techniques and even treatments for cancer are certainly inherently flawed. It should come down to the availability of GOOD information and GREAT, COMPASSIONATE advice on the part of the clinician. In the end the choice has to be made by the patient. Then again, the definition of "informed" these days is sketchy at best...

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