As I suggested earlier, the real question is, Does cancer testing reduce the rate at which people die from cancer? And the simple truth is, that can be hard to know.
Let me begin by saying that there's good news on the cancer front. Since 1950 mortality has fallen by over fifty percent for cancers of the stomach, cervix, uterus, testis, and Hodgkin's disease, a cancer of the lymph glands. And the mortality for cancers in children is a third of what it was 50 years ago. There isn't any ambiguity about how to interpret these dramatic declines. They are really good news.
But it's hard to know why cancer mortality has fallen. Too often the assumption is that declining mortality is a result of cancer testing. In point of fact, though, a number of explanations are possible. The first may have nothing related to medical care at all: reduced exposure to cancer-causing agents. Declining use of certain food preservatives, for example, is the explanation given by most experts for the fall in stomach cancer mortality.
The second has everything related to medical care but nothing related to earlier detection: we have gotten better at treating cancer when it first causes symptoms. Here is the predominant explanation for falling mortality in the cancers of childhood, Hodgkin's disease, and testicular cancer. The third is due to earlier detection but has nothing related to testing: patients with symptoms are increasingly aware of the significance of seeking care sooner rather than later.
Older women's recognition that vaginal bleeding is abnormal after menopause, for example, may help explain the decline in uterine cancer. The final explanation is cancer testing: testing finds small, asymptomatic cancers that were destined to kill, cancers that are treatable at the time of testing but not after symptoms appear. Cancer testing, specifically the Pap smear, is the standard explanation given for the fall in cervical cancer although other factors, such as improved hygiene generally and less std, undoubtedly are likely involved as well. (In addition, much of the value of the Pap smear may have less to do with pathologists or more precisely, cytologists examining cells under a microscope than with doctors actually seeing the cervix.)
Mortality for some other cancers is falling as well, if less dramatically. Since 1950 mortality from neck and head cancer, thyroid cancer, and bladder cancer are all down. Although some environmental reasons may apply, my guess is that these declines are best explained by a mix of two factors: people with symptoms are seeking care earlier, and better treatment is available. Cancer testing is not a viable explanation, as no systematic testing exists for these cancers. Then there is colon and breast cancer, for which mortality is down by 25% and 15%, respectively. In the two caser a systematic effort is being made to detect early disease. Are these two examples of where testing is really helping?
To be perfectly honest, it's hard to know. Most doctors (myself included) believe that an array of tests fecal occult blood test, sigmoidoscopy, barium enemas, and colonoscopy really are helping to reduce deaths from colon cancer. And the incidence of colon cancer is up only slightly, which means testing doesn't detect lots of pseudodisease. Still, colon cancer testing does have problems, most notably excessive repetitive testing annual colonoscopies following the detection of 1 or 2 polyps, for example.
Why there has been a small, but real, decline in breast cancer mortality is one of the hottest topics in medicine. Treatment really improved with the advent of hormonal therapy. And it is obvious that women have become increasingly aware of the significance of having new lumps evaluated, often with a diagnostic mammogram. The usefulness of performing screening mammograms, however that is, on women who don't have lumps is a complicated subject, and the question of whether finding breast cancers that are too small to be felt hurts more than it helps remains open to debate.
Then you have the not so good news. Prostate and ovarian cancer mortality remain essentially unchanged in the last 50 years, while mortality is rising for cancers of the esophagus, liver, pancreas, kidney, and brain and for melanoma. Finally, the worst news: in the last 50 years, the rate at which people die from lung cancer is up more than threefold. The explanation for this last increase can be summed up in one word: smoking.
As I hope this article makes clear, of the three major cancer statistics five-year survival, incidence, and mortality mortality is an essential. It's just the best statistic for making judgments about how well we are doing in controlling cancer. And it is the least subject to spurious influence of new cancer testing that inflates both incidence and fiveyear survival. Simply put: it is much easier to be certain about who dies of cancer than it is to be certain about who really has the disease and when it actually starts.
But even mortality can be problematic. Although there is no ambiguity about which people die and when, there is some ambiguity about why they die. First, simply knowing that a person has cancer influences how doctors determine the reason for death. So by finding more cancer, cancer testing may indirectly inflate apparent cancer mortality. Ironically, testing is likely responsible for much of the rising mortality of cancers we just couldn't "see" 50 years ago: cancer of the esophagus, liver, pancreas, kidney, and brain.
Then there's the question of what counts as a cancer death. If we are really interested in capturing true progress in cancer, cancer mortality should include not only deaths from cancer but also deaths from cancer treatment. In fact, ideally any deaths that occurred as a consequence of looking for cancer should be included as well. Consider an imaginary population with 500 deaths per 100,000 from cancer, with no early detection or treatment program in place. Afew years later the death rate is 400 from the cancer, 40 from surgery for the cancer, 60 from chemotherapy/ radiation, and 10 from the testing and biopsy process. Would you say there is progress? I doubt it.
Most deaths during or immediately following cancer surgery do get counted in cancer mortality, but not all. It is much more difficult to know whether chemotherapy and radiation deaths are being properly counted (and to be fair, it is very difficult to do). And we're not monitoring the deaths, however few, that are a consequence of the testing process. So even with our best statistic, there is room for improvement.
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