Cancer. It’s a word that inspires fear in patients when they contemplate the effect on their lives. Reasonably, many of us try to minimize our risk of getting this dreaded disease.

Screening plays a major role in trying to avoid cancer deaths by emphasizing early detection – finding tumors early, where the chance of cancer spread and death is as low as possible. Trying to screen everyone so we can maximize the chance of a cure makes sense but, as usual, the devil is in the details.

In 2016, there were an estimated 1.65 million new cancer cases diagnosed in the United States, according to the National Cancer Institute. Cancer was also responsible for the deaths of more than 595,000 Americans last year.

Dr. Robin Schoenthaler, radiation oncologist at the MGH Department of Radiation Oncology at Emerson Hospital in Concord, Mass., notes that while the screening process is an important first step in determining if cancer is present in the body, there are different guidelines published by physician groups that include different recommendations.

There are screenings for all types of cancer, and there are specific screening guidelines for four of the most common cancers: breast, lung, prostate and colon. With lung cancer, it’s simple: CT screening is only recommended in people with a history of long-term smoking. But when it comes to screening for the other cancer types, Dr. Schoenthaler says that’s where differences of opinion come into play.

When it comes to breast cancer screenings, for example, there are several sets of guidelines used by physicians. Three of the guidelines have been released by the U.S. Preventive Services Task Force (USPSTF), The American Cancer Society, and the American Congress of Obstetricians and Gynecologists (ACOG). Each of these groups has its own particular guidelines for when women should begin to receive mammograms.

ACOG recommends women begin annual screening at the age of 40. ACS suggests annual screening should begin at age 45 and continue through to age 54. Women ages 55 and up should be screened every two years, according to the ACS guidelines. The USPSTF guidelines are the loosest of the three sets, calling for women ages 40 to 49 to consult with their doctors about the necessity of mammograms. Women ages 50 to 74 should receive a mammogram every two years, according to the USPSTF guide.

Dr. Schoenthaler says there are numerous factors that breed the controversies, but the discrepancy between the guidelines boils down to statistics and how data is measured. She says there are numerous false positives that can read out from mammograms conducted on women ages 40 to 49. Those false positives spark anxiety and biopsies that may be totally unnecessary, which helps generate the controversies, she adds.

“Without question, mammograms do save lives, but statisticians and epidemiologists balance that against all the other concerns,” Dr. Schoenthaler says.

The same is true for prostate cancer screenings in men. Dr. Schoenthaler was in medical school when screening for prostate-specific antigen (PSA) began to be widely used. At the time, physicians thought it was “a miracle – the first test ever that could detect signs of cancer in the blood.” However, over the years the controversies have increased.

“The number of lives saved with PSA is small,” Dr. Schoenthaler says. “Now if that life is yours, that’s everything. But the reality is, there’s a significant amount of over-diagnosis with every man screened for PSA.”

Too often, a slight elevation in the PSA leads to unnecessary biopsies being performed. Most of the time, a positive biopsy leads to treatment with radiation or surgery, which can lead to serious and lasting complications including incontinence, rectal problems, or impotence. Dr. Schoenthaler says all groups recommend patients have serious talks with their physicians about the possible risks and benefits before ordering a PSA test.

Colonoscopies, which are used to determine if there are pre-cancerous polyps and cancerous lesions in the colon, unfortunately also have different guidelines that have been issued by different medical groups. The beauty of colonoscopies is what they can find.

In a presentation Dr. Schoenthaler delivered last year, she described screenings as “a blunt instrument in the battle against cancer.” But, despite the false positives, the conflicting guideline recommendations and over-diagnosis, Dr. Schoenthaler emphasizes and assures that screenings do save lives.

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