Breast cancer testing in the nation's oldest patients is highly unlikely to detect lethal disease, hugely expensive and more likely to harm than help since any follow-up testing and treatment is often invasive. Nearly 1 in 5 women with severe cognitive impairment including older patients are still get regular mammograms, according to the American Journal of Public Health even though they're not recommended for people with a limited life expectancy and 55% of older men with a high risk of death over the next decade still get PSA tests for prostate cancer, according to a study in JAMA Internal Medicine.

Among people in their 70s and 80s, cancer screenings often detect slow-growing tumours that are unlikely to cause problems in patients' lifetimes. Such patients often die of something else long before their cancers would ever have become a threat. Patients with dementia rarely live longer than a few years. It generally takes about 10 years to see benefit from cancer screening, at least in terms of a mortality benefit.

In some cases, women are being screened for tumours in organs they no longer have. In a study of women over 30, nearly two-thirds who had undergone a hysterectomy got at least one cervical cancer screening, including one-third who had been screened in the past year, according to a study in JAMA Internal Medicine.

Approximately 9% of women with advanced cancer received mammograms and 6% received cervical cancer screening, according to a study of Medicare recipients over age 65. Among men on Medicare with incurable cancer, 15% were screened for prostate cancer.Testing can lead to anxiety, invasive follow-up procedures and harsh treatments. In patients well into their 80s, with other chronic conditions, it's highly unlikely that they will receive any benefit from screening, and more likely that the harms will outweigh the benefits.

By screening patients near the end of life, doctors often detect tumours that don't need to be found and treated. Researchers estimate that up to two-thirds of prostate cancers are overdiagnosed, as are a third of breast tumours. A variety of medical specialities from the American College of Surgeons to the Society of General Internal Medicine have advised doctors against screening patients with limited time to live.

A coalition of patient advocates, employers and others included prostate screenings in men over age 75 in its list of the top five "low-value" medical procedures. Prostate cancer screening in men over 75 cost Medicare at least $145 million a year, according to a study in the journal Cancer. Mammograms in this age group cost the federal health plan for seniors more than $410 million a year, according to a 2013 study in JAMA Internal Medicine.

And while cancer screenings generally aren't expensive—a mammogram averages about $100—they can begin a series of follow-up tests and treatments that add to the total cost of care. Most spending on unnecessary medical care stems not from rare, big-ticket items, such as heart surgeries, but cheaper services that are performed much too often, according to an October study in Health Affairs.

Many older patients expect to continue getting screened, said Dr Mara Schonberg, an associate professor at Harvard Medical School and Boston's Beth Israel Deaconess Medical Center. It's jarring for someone who's been told every year to get screened and then at age 75 you tell them to stop, she said.