January 1, 2018


Too much screening has misled us about real cancer risk factors, experts say (SHARON BEGLEY, JANUARY 1, 2018, STAT)

The problem is especially clear in prostate, breast, and thyroid cancers, all of which are scrutiny dependent.

Men whose relatives developed prostate cancer are more likely to get PSA and other screening tests, either because they request them or because their physicians, noting their family histories, order them. Men with no such family history are less likely to be screened. Some men who get screened for prostate cancer and who are found to have elevated PSA levels undergo a prostate biopsy; some of those biopsies find cancer. (More than half of such cancers are so slow-growing that they don't affect health or longevity.) Men who don't get screened are less likely to have biopsies and so are less likely to be diagnosed with prostate cancer -- not because they develop the disease at a lower rate but because they get screened at a lower rate. What you don't look for, you don't find.

"If we biopsied men without a family history of prostate cancer at the same rate that we biopsy men with a family history, we'd find more prostate cancer in them as well," Welch said. "Family history influences how hard we look for prostate cancer and therefore how much we find. The risk factor becomes a self-fulfilling prophecy."

A 2016 study of increased prostate cancer screening in men with a family history of the disease concluded that the risk due to family history has been overestimated by nearly half. "The risk factor of family history is spuriously strengthened because men with a family history are exposed to greater scrutiny," write Welch and Dr. Otis Brawley, chief medical officer of the American Cancer Society, in the Annals report.

"There is a flaw in this logic" of identifying risk factors "on the basis of how many cancers we find," agreed Dr. Peter Albertsen of UConn Health, an expert in prostate cancer.

In breast cancer, women who live in neighborhoods with the highest 20 percent of education and income are twice as likely to be diagnosed with that disease, a 2017 study found. That seemed to confirm reports of breast-cancer hot spots in some of America's wealthiest areas, leading the government and others to spend tens of millions of dollars to find out why. Those studies came up empty: they found no association between rates of breast cancer and proximity to a hazardous waste site or pesticide exposure, for instance.

Wealthier, better educated women are, however, more connected to the health care system and therefore get more mammograms, breast ultrasounds, and MRIs. The more scrutiny, the more likely that harmless cases of breast cancer are found. (The idea of "harmless" breast cancer sounds like an oxymoron, but an estimated one-half of breast cancers detected by screening would never cause problems even if undetected and untreated.)

Breast tumors found by imaging are much more likely to be harmless than those discovered by women or their physicians finding a breast lump. Income and education are therefore less likely to be a true risk factor for breast cancer and more likely to be a "risk factor" for undergoing screening. If poorer, less educated women were screened for breast cancer at the same rate as wealthier, better educated women, the socioeconomic risk factor would likely vanish.

Posted by at January 1, 2018 7:00 PM