“Mom — what are you talking about?”

My friend was on a family vacation when her mother mentioned she had to get her annual mammogram. My friend continued: “You don’t need a mammogram! You’re 88!”

Her mother gave her a withering look: “What? I’m so old at 88, you want me to die of breast cancer?”

So ingrained is the annual mammogram habit in this country that any challenge to it is met with a combination of scorn and outrage.

We belong to the pink ribbon sisterhood that worked hard to strike down the stigma of breast cancer and get better care. We walk for the cure. We lobby Congress for research funds. We demand coverage of screening, including high-tech digital mammography. In the last 20 years, deaths from breast cancer have gone down by about 30 percent.

But what role has screening played in this decline?

At a forum in March at the Harvard School of Public Health in Boston, physicians and policy officials debated the question “Mammograms: Who in the world are they good for?” I was the moderator, and at the end of the afternoon, I came away concluding that it’s time to rethink our policies on screening.

Mette Kalager, a surgeon at Oslo University Hospital and a visiting scientist at the Harvard School of Public Health, told the forum about a study she had led in Norway.

The researchers looked at the records of 40,075 women who received diagnoses of breast cancer between 1986 and 2005. Some had been screened every two years. Others had not been screened; their cancers were been detected by physical examination. Both groups were treated by teams of specialists. Over the 20-year period of the study, both groups saw a decline in death rates from the disease.

By comparing the groups, researchers determined that only about a third of this decline was due to screening. Most of it was due to state-of-the art treatment and comprehensive care. Previous studies had suggested a greater impact from screening, and the study, published in the New England Journal of Medicine in September, caused a stir in the breast cancer community.

A little history is in order. When mammography screening got underway in the United States 40 years ago, it put breast cancer on the public agenda. Catch-it-early-when-it’s-curable became a mantra of hope. Since then, treatments have improved, and the understanding of breast cancer has changed. Perhaps more important than the timing of detection is the biology of the cells. “There are some very tiny cancers that are just bad biology and are destined to relapse, no matter how early you find them,” Julie Gralow, a professor of oncology at the University of Washington Medical School, told the Harvard forum.

And some cancers don’t progress even when they are found late. “I’ve had patients who have had very aggressive, large cancers, [which,] for one reason or another, they have ignored,” continued Gralow. “And still years later, it never spreads. It doesn’t come back. . . . We’re struggling to understand the biology.”

Diagnosing a cancer early often leads to more-conservative treatment (such as lumpectomy instead of mastectomy), a great advantage to patients. But the annual mammogram may not be as important as it once was in stemming the death toll. “The evidence seems to be that mammography screening plays less and less of a role in reducing mortality in countries of the Western world,” Kalager said.

That may be true for older women in particular. In Europe, mammography screening is recommended only for women ages 50 to 69. Yet when Kalager and her colleagues studied breast cancer patients ages 70 to 84, they saw a reduction in mortality that “was largely the same” as in younger women who were screened. The key for both groups was access to good care.

But Felicia Knaul, director of the Harvard Global Equity Initiative, offered a different view: “I was diagnosed with a breast cancer 31 / 2 years ago in my first baseline mammogram at age 41, ” she said. “If anything saved my life, in addition to [expert care], it is that mammogram.”

The room went quiet. How to resolve the experience of Knaul with the findings of a study based on more than 40,000 women? Furthermore, as Knaul pointed out, many women, especially in developing countries, do not have access to the state-of-the art care.

Such is the conundrum for policymakers in setting health guidelines: Personal anecdote often clashes with wider research. But screening policies should be based on evidence from large-scale population studies: the greatest good for the greatest number.

The United States has the most expansive mammography screening standards in the world, starting at age 40 and continuing every year. But more is not necessarily better in health care.

Wide-net screening can cause harm, leading to over-detection, over-diagnosis and unnecessary treatment, according to Kalager and other researchers. Once a woman has a suspicious mammogram, she gets on a medical train and can’t get off until the doctor-conductor gives the all-clear signal. Often that requires just a repeat test. But some women are treated for cancers that are not invasive or are too slow-growing to endanger their health. They undergo surgery or drugs or radiation with side effects such as blood clots, breathing problems, lymphedema and high blood pressure.

“I don’t know how to weigh the over-detection piece,” said Gralow. “We clearly have to sort that one out.”

Yes, there’s a lot of sorting out to do. My friend’s mother, who believed in annual screening, obviously managed her health pretty well. She never got breast cancer and lived to age 94. But my friend was also right: Research is on her side.