If screening’s benefits have been overstated, its potential harms are little discussed. According to a survey of randomized clinical trials involving 600,000 women around the world, for every 2,000 women screened annually over 10 years, one life is prolonged but 10 healthy women are given diagnoses of breast cancer and unnecessarily treated, often with therapies that themselves have life-threatening side effects. (Tamoxifen, for instance, carries small risks of stroke, blood clots and uterine cancer; radiation and chemotherapy weaken the heart; surgery, of course, has its hazards.)

Many of those women are told they have something called ductal carcinoma in situ (D.C.I.S.), or “Stage Zero” cancer, in which abnormal cells are found in the lining of the milk-producing ducts. Before universal screening, D.C.I.S. was rare. Now D.C.I.S. and the less common lobular carcinoma in situ account for about a quarter of new breast-cancer cases — some 60,000 a year. In situ cancers are more prevalent among women in their 40s. By 2020, according to the National Institutes of Health’s estimate, more than one million American women will be living with a D.C.I.S. diagnosis.

D.C.I.S. survivors are celebrated at pink-ribbon events as triumphs of early detection: theirs was an easily treatable disease with a nearly 100 percent 10-year survival rate. The thing is, in most cases (estimates vary widely between 50 and 80 percent) D.C.I.S. will stay right where it is — “in situ” means “in place.” Unless it develops into invasive cancer, D.C.I.S. lacks the capacity to spread beyond the breast, so it will not become lethal. Autopsies have shown that as many as 14 percent of women who died of something other than breast cancer unknowingly had D.C.I.S.

There is as yet no sure way to tell which D.C.I.S. will turn into invasive cancer, so every instance is treated as if it is potentially life-threatening. That needs to change, according to Laura Esserman, director of the Carol Franc Buck Breast Care Center at the University of California, San Francisco. Esserman is campaigning to rename D.C.I.S. by removing its big “C” in an attempt to put it in perspective and tamp down women’s fear. “D.C.I.S. is not cancer,” she explained. “It’s a risk factor. For many D.C.I.S. lesions, there is only a 5 percent chance of invasive cancer developing over 10 years. That’s like the average risk of a 62-year-old. We don’t do heart surgery when someone comes in with High cholesterol. What are we doing to these people?” In Britain, where women are screened every three years beginning at 50, the government recently decided to revise its brochure on mammography to include a more thorough discussion of overdiagnosis, something it previously dispatched with in one sentence. That may or may not change anyone’s mind about screening, but at least there is a fuller explanation of the trade-offs.

In this country, the huge jump in D.C.I.S. diagnoses potentially transforms some 50,000 healthy people a year into “cancer survivors ” and contributes to the larger sense that breast cancer is “everywhere,” happening to “everyone.” That, in turn, stokes women’s anxiety about their personal vulnerability, increasing demand for screening - which, inevitably, results in even more diagnoses of D.C.I.S. Meanwhile, D.C.I.S. patients themselves are subject to the pain, mutilation, side effects and psychological trauma of anyone with cancer and may never think of themselves as fully healthy again.

Yet who among them would dare do things differently? Which of them would have skipped that fateful mammogram? As Robert Aronowitz, the medical historian, told me: “When you’ve oversold both the fear of cancer and the effectiveness of our prevention and treatment, even people harmed by the system will uphold it, saying, ‘It’s the only ritual we have, the only thing we can do to prevent ourselves from getting cancer.’ ”

What if I had skipped my first mammogram and found my tumor a few years later in the shower? It’s possible that by then I would have needed chemotherapy, an experience I’m profoundly thankful to have missed. Would waiting have affected my survival? Probably not, but I’ll never know for sure; no woman truly can. Either way, the odds were in my favor: my good fortune was not just that my cancer was caught early but also that it appeared to have been treatable.

Other researchers are excited about the prospect of fighting or preventing cancer by changing the “microenvironment” of the breast — the tissue surrounding a tumor that can stimulate or halt its growth. Susan Love likened it to the way living in a good or bad neighborhood might sway a potentially delinquent child. “It may well be,” she told me, “that by altering the ‘neighborhood,’ whether it’s the immune system or the local tissue, we can control or kill the cancer cells.” Taking hormone-replacement therapy during menopause, which was found to contribute to escalating rates of breast cancer, may have been the biological equivalent of letting meth dealers colonize a street corner. On the other hand, a vaccine, the current focus of some scientists and advocates, would be like putting more cops on the beat.