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.

Imaging Aids Reduce Diagnostic Accuracy

I've sometimes been described as a Luddite because of my resistance to adopt certain technologies (though my iPod and laptop would beg to differ). In a recent case of man vs. machine published in the New England Journal of Medicine compares mammograms subjected to computer-aided detection (CAD) to those screened without computer assistance. CAD software, approved for use in 1998, analyzes mammogram images and marks suspicious areas which are then reviewed by a radiologist. The NCI sponsored study found that CAD did not increase cancer-detection rate, in contrast to early studies that showed a 10-15% increase in diagnosis rate - similar to the increase found with a second human opinion. Instead, this much more comprehensive study found a significant increase in false positive rate, resulting in more call-backs and biopsies, and increased burden on the system and ulitmately an increase in cost for breast screening.

From the NCI press release:

"This study points out the need for the use of other techniques to find cancer at its earliest stages. NCI is incorporating techniques for imaging at the molecular level into many of its studies and is also conducting studies to improve the use of CAD and conventional mammography," said John E. Niederhuber, M.D., NCI Director. "In the end, technology facilitates screening. Ultimately, treatment requires radiologists working with the examining physician and the responsible surgeon to put everything together. We worry about false positives, but we certainly don't want to miss any cancers, either."