For more than 15 years, I’ve been warning patients about the downside of mammograms, PSA testing, and the overall concept of cancer screening. It hasn’t been a popular position. Today, however, there’s a small but growing band of researchers, clinicians, and expert panels who are speaking out against the unbridled use of these tests. One of them, H. Gilbert Welch, MD, a professor at Dartmouth Medical School, has laid out very persuasive arguments in an aptly titled book, Should I Be Tested for Cancer? Maybe Not and Here’s Why. In this straightforward and well-referenced book, Dr. Welch raises several concerns about cancer screening.
1. Few People Benefit From Screening
For starters, the majority of folks who are screened receive no benefit. That’s because, despite scary statistics, most people will not get cancer. Let’s look at breast cancer as an example.
According to government statistics, the absolute risk of a 60-year-old woman dying from breast cancer in the next 10 years is 9 in 1,000. If regular mammograms reduce this risk by one-third-a widely cited but by no means universally accepted claim-her odds fall to 6 in 1,000. Therefore, for every 1,000 women screened, three of them avoid death from breast cancer, six die regardless, and the rest? They can’t possibly benefit because they weren’t going to die from the disease in the first place.
If mammograms worked as touted, death from breast cancer would be rare, since three-quarters of American women 40 and older get regular screenings (a total of 33.5 million per year). The modest decline in the death rate from the mid-1970s, when mammography was introduced, through the present can be attributed to factors other than screening, such as changes in treatment and the dramatic decrease in the use of Premarin and other cancer-promoting hormone replacement drugs. It doesn’t take a rocket scientist to figure out that mammograms do not substantially reduce risk of death from breast cancer.
2. The Most Deadly Cancers Are Missed
The flip side is that some people who are screened get cancer and die anyway. Test results aren’t always accurate. Sometimes cancer is there, but it’s missed (false negatives). In the case of mammograms, it could be a question of a poor-quality test or a radiologist who overlooked something. Even experienced radiologists don’t always interpret test results the same, and sometimes they just plain get it wrong.
The most likely reason that cancer is overlooked, however, is due to the nature of cancer itself. The deadliest cancers grow very rapidly. Screening can detect slow-growing cancers in their early stages, but you can see how aggressive cancers could be missed if you’re only looking for them once a year. Depending on the cancer’s growth cycle, it could crop up just months after screening and be far advanced by the time the next test rolls around.
3. The Pitfalls of False Positives
Far more common than false negatives are false positives-those cancer scares that occur when you’re told that your test is suspicious but, after further evaluation, turns out to be nothing. False positives lead to confirmatory testing such as ultrasound of the breast and prostate, CT scan of the lung, colonoscopy, and colposcopy of the cervix. These tests are at best inconvenient and at worst extremely unpleasant, as anyone who’s had a colonoscopy knows. They also often lead to biopsies, which are far more invasive and could possibly promote the spread of cancer.
Unfortunately, false positive rates are incredibly high. For mammography, it’s close to 10 percent. For every 100 women screened, 10 will require further workup. If you repeat this screening test every year for 10 years, your cumulative risk of having at least one false positive rises to 65 percent. This means that more than half of all women will get the terrifying news that their mammogram is abnormal-the first step on the slippery slope of intervention.
False positive rates are high for PSA as well, especially among older men. Some estimate that three-quarters of men who have a prostate biopsy based on an elevated PSA level do not have cancer. And lifetime false-positive risk for Pap smears is 75 percent.
Another consideration is the psychological trauma of cancer screening. Being told you might have cancer is a harrowing experience, and the lag time between retesting and getting a clean bill of health can be months.
4. Unnecessary Treatment
Even worse than the sound and fury created by false positives is unnecessary treatment. Yes, some lives are saved due to early detection and treatment. But not all cancers are the same. Some are deadly, treated or not; others are not fatal regardless of treatment. Dr. Welch calls the latter pseudodisease-small, slow-growing or nonprogressive cancers that you’d never know existed were it not for screening tests. Yet all too often, these innocuous tumors are attacked with a vengeance, often to the detriment of patients.
A prime example is prostate cancer. Since 1975, its incidence has more than doubled. But rather than having an epidemic of prostate cancer, what we have is an epidemic of detection. Although many more men are being diagnosed and treated, the death rate from prostate cancer has held steady at 3 percent.
It’s human nature, when given a diagnosis of cancer, to want to get rid of it. But prostate cancer treatment is not benign. Surgical complications include difficulty urinating (17 percent), urinary incontinence (28 percent), and inability to have an erection (more than 50 percent). Radiation damages the rectum and can cause diarrhea and bowel urgency. Side effects of androgen suppression range from sexual dysfunction to risk of diabetes and heart disease.