Cancer Screening: An Unbiased Appraisal
Julian Whitaker, MD
Anne is a good patient. She sees her doctor for regular checkups, has yearly mammograms, Pap tests, and colon cancer screenings, and she even paid for a full-body CT scan out of her own pocket. She figures she’s doing everything she can to make sure she doesn’t get cancer.
Truth is, Anne is doing nothing to prevent cancer. Although cancer screening is billed as a preventive service that saves lives, the best it can do is detect disease in its early stages, when it is supposedly easier to treat. Nevertheless, every year millions of Americans dutifully line up for their screenings, completely unaware that they may be doing more harm than good.
For more than 15 years, I’ve been writing 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 valid 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 and to biopsies, which are 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.
Much of this treatment is completely unwarranted. Remember, the majority of prostate cancer is pseudodisease. Most men die with it, not of it.
What Tests Should You Get?
So which tests should you get and when should you get them? It depends on who you listen to. Unfortunately, there’s no clear consensus among expert panels and advocacy groups, so confusion reigns.
I hesitate to make blanket recommendations. However, before you have a test, I strongly encourage you to understand both the pros—the slim but potentially lifesaving possibility that early-stage, clinically significant cancer will be found and treated—and the cons—the high risk of false positives, additional testing, anxiety, and unnecessary treatment. That way, you’ll be better prepared to deal with the outcome, whatever it may be.
PSA for prostate cancer. PSA is the most controversial of all screening tests because of very high false positive rates and rampant over-treatment. The US Preventive Services Task Force has concluded that “the current evidence is insufficient to assess the balance of benefits and harms of prostate cancer screening in men younger than age 75 years.” In August 2008, this group also urged physicians to stop testing PSA in men 75 and older.
Mammograms for breast cancer. Mammograms carry the most emotional baggage—it’s downright unpatriotic to badmouth these tests. Several randomized controlled trials have looked at screening mammography. Some support its utility, some don’t. As I mentioned earlier, more than one in two women who have yearly mammograms for 10 years will have a false positive. Furthermore, many of the cancers detected and unnecessarily treated are pseudodisease.
Fecal occult blood tests and colonoscopy for colon cancer. Three randomized studies suggest that fecal occult blood tests lower chances of dying from colon cancer by 15 to 30 percent. However, false positives are very common. Regarding colonoscopy, the Preventive Services Task Force has concluded, “It is unclear whether the increased accuracy of colonoscopy…offsets the procedure’s additional complications, inconvenience, and costs.”
Pap smears for cervical cancer. National Cancer Institute guidelines recommend Pap smears once every three years. Most experts agree that women 65 to 70 who have had three normal tests in a row and are at low risk can stop having them, as well as those who’ve had a hysterectomy. Be aware that lifetime false positive rates are extremely high and that many doctors inexplicably order Pap smears annually for women of all ages.
Chest X-rays for lung cancer. Three clinical trials have shown that routine chest X-rays do not reduce risk of death from lung cancer. No group stands behind routine screening at this time.
Genetic tests for cancer risk. Cancer is not caused by a single gene defect, and a positive test doesn’t necessarily mean you will get cancer. Moreover, twin studies emphasize the role of lifestyle and environmental factors in development of the disease.
Other cancer screening tests. Other screening tests that have yet to be shown in randomized trials to save lives include ultrasounds and CA-125 for ovarian cancer, skin exams for melanoma, and head and body scans for cancer of the brain and abdomen.
I understand that this is an emotionally charged issue. Cancer is scary and the treatments for it are as frightening as the disease itself. If you have symptoms of cancer, by all means see a doctor and discuss appropriate testing.
Otherwise, think twice. If your physician orders a cancer screening test, question its necessity. Doctors sometimes suggest these tests for all the wrong reasons: fears of malpractice, financial incentives, and even patient demand. Find out what course would be recommended if your results were positive. Then review the information above, read Dr. Welch’s book, and make your own educated decision.
Next time you hear that someone who died of cancer would have been saved if only he’d had regular testing, realize that’s nothing more than unsubstantiated opinion. And, whatever you do, don’t let anyone make you feel irresponsible if you elect not to undergo cancer screening.
- SEER. Cancer of the breast. National Cancer Institute. http://seer.cancer.gov/statfacts/html/breast.html Accessed Sept. 2, 2008.
- US Preventive Services Task Force. Guide to Clinical Preventive Services. http://www.ahrq.gov/clinic/cps3dix.htm#cancer. Accessed Aug 25, 2008.
- Welch HG. Should I Be Tested for Cancer? Berkeley, CA: University of California Press; 2004.
Modified from Health & Healing with permission from Healthy Directions, LLC. Photocopying, reproduction, or quotation strictly prohibited without written permission from the publisher. To subscribe to Health & Healing, click here.