"The myth of early detection"

This April column by Newsweek writer Sharon Begley made a big impression on me and I've often thought of it since. Here's an excerpt:

. . . the truly infuriating, head-scratching thing about all early-detection studies: that the results are not an unambiguous, slam-dunk positive. If the hype is right, then finding a tumor when it is small should mean a better chance that surgery, radiation and/or chemotherapy will eradicate it, allowing you to live until something else kills you. Early detection should produce clear, unquestionable benefits.

Yet it doesn't. Not the PSA [prostate cancer test], not early detection of lung or testicular or pancreatic cancer, or glioblastomas, a type of brain cancer. Even mammography is iffy, since trials showing a decrease in mortality were done before the age of adjuvant therapy. Colonoscopy might cut mortality, but it has never been tested in a randomized, controlled trial, notes Barnett Kramer of the National Institutes of Health, lead author of one of the new PSA studies. The Pap test for cervical cancer and the fecal occult blood test for colorectal are about the only screening tests shown to decrease mortality from the cancer they target. If the failure of most early detection to strongly affect whether you live or die makes no sense to you, you're not alone. "The medical community has done such an extraordinary job getting out the message that early detection is tantamount to cure, it's incorporated into people's bone marrow," says Kramer.

One reason early detection doesn't make a bigger difference is that, absent effective therapy, it hardly matters when a tumor is found: early or late, you're doomed. This is pretty much the case, sadly, for glioblastomas and pancreatic cancer. But the benefits of early detection also vanish if therapy is so terrific, or the malignancy so slow-growing, that the cancer can be vanquished even if caught late. This describes many testicular cancers. It is for cancers such as breast and colorectal, where therapies sometimes succeed and sometimes fail, that early detection should help.

But the natural progression of cancers also undercuts the value of early detection. "All the common cancers have a spectrum of aggressiveness," says Kramer. Some are slow-growing, while other cancers of the same organ are aggressive and deadly, speeding from birth to an advanced stage before you know what hit you. If you look for cancer in asymptomatic people—as screening does—you are much more likely to find an indolent one for the simple reason that indolent cancers, by definition, spend more time in an early, nonthreatening stage, whereas aggressive cancers speed through that early stage. "You may pick up tumors that can be cured, but which never needed to be treated in the first place," says Kramer. Failing to detect an indolent cancer early doesn't necessarily put you at much of a disadvantage.