BE AWARE, BE VERY AWARE:

Breast cancer in your breast doesn't kill you; the disease becomes deadly when it metastasizes, spreading to other organs or the bones. Early detection is based on the theory, dating back to the late 19th century, that the disease progresses consistently, beginning with a single rogue cell, growing sequentially and at some invariable point making a lethal leap. Curing it, then, was assumed to be a matter of finding and cutting out a tumor before that metastasis happens.

The thing is, there was no evidence that the size of a tumor necessarily predicted whether it had spread. According to Robert Aronowitz, a professor of history and sociology of science at the University of Pennsylvania and the author of "Unnatural History: Breast Cancer and American Society," physicians endorsed the idea anyway, partly out of wishful thinking, desperate to "do something" to stop a scourge against which they felt helpless. So in 1913, a group of them banded together, forming an organization (which eventually became the American Cancer Society) and alerting women, in a precursor of today's mammography campaigns, that surviving cancer was within their power. By the late 1930s, they had mobilized a successful "Women's Field Army" of more than 100,000 volunteers, dressed in khaki, who went door to door raising money for "the cause" and educating neighbors to seek immediate medical attention for "suspicious symptoms," like lumps or irregular bleeding.

The campaign worked -- sort of. More people did subsequently go to their doctors. More cancers were detected, more operations were performed and more patients survived their initial treatments. But the rates of women dying of breast cancer hardly budged. All those increased diagnoses were not translating into "saved lives." That should have been a sign that some aspect of the early-detection theory was amiss. Instead, surgeons believed they just needed to find the disease even sooner.

Mammography promised to do just that. The first trials, begun in 1963, found that screening healthy women along with giving them clinical exams reduced breast-cancer death rates by about 25 percent. Although the decrease was almost entirely among women in their 50s, it seemed only logical that, eventually, screening younger (that is, finding cancer earlier) would yield even more impressive results. Cancer might even be cured.

That hopeful scenario could be realized, though, if women underwent annual mammography, and by the early 1980s, it is estimated that fewer than 20 percent of those eligible did. Nancy Brinker founded the Komen foundation in 1982 to boost those numbers, convinced that early detection and awareness of breast cancer could have saved her sister, Susan, who died of the disease at 36. Three years later, National Breast Cancer Awareness Month was born. The khaki-clad "soldiers" of the 1930s were soon displaced by millions of pink-garbed racers "for the cure" as well as legions of pink consumer products: pink buckets of chicken, pink yogurt lids, pink vacuum cleaners, pink dog leashes. Yet the message was essentially the same: breast cancer was a fearsome fate, but the good news was that through vigilance and early detection, surviving was within their control.

By the turn of the new century, the pink ribbon was inescapable, and about 70 percent of women over 40 were undergoing screening. The annual mammogram had become a near-sacred rite, so precious that in 2009, when another federally financed independent task force reiterated that for most women, screening should be started at age 50 and conducted every two years, the reaction was not relief but fury. After years of bombardment by early-detection campaigns (consider: "If you haven't had a mammogram, you need more than your breasts examined"), women, surveys showed, seemed to think screening didn't just find breast cancer but actually prevented it.

At the time, the debate in Congress over health care reform was at its peak. Rather than engaging in discussion about how to maximize the benefits of screening while minimizing its harms, Republicans seized on the panel's recommendations as an attempt at health care rationing. The Obama administration was accused of indifference to the lives of America's mothers, daughters, sisters and wives. Secretary Kathleen Sebelius of the Department of Health and Human Services immediately backpedaled, issuing a statement that the administration's policies on screening "remain unchanged."

Even as American women embraced mammography, researchers' understanding of breast cancer -- including the role of early detection -- was shifting. The disease, it has become clear, does not always behave in a uniform way. It's not even one disease. There are at least four genetically distinct breast cancers. They may have different causes and definitely respond differently to treatment. Two related subtypes, luminal A and luminal B, involve tumors that feed on estrogen; they may respond to a five-year course of pills like tamoxifen or aromatase inhibitors, which block cells' access to that hormone or reduce its levels. In addition, a third type of cancer, called HER2-positive, produces too much of a protein called human epidermal growth factor receptor 2; it may be treatable with a targeted immunotherapy called Herceptin. The final type, basal-like cancer (often called "triple negative" because its growth is not fueled by the most common biomarkers for breast cancer -- estrogen, progesterone and HER2), is the most aggressive, accounting for up to 20 percent of breast cancers. More prevalent among young and African-American women, it is genetically closer to ovarian cancer. Within those classifications, there are, doubtless, further distinctions, subtypes that may someday yield a wider variety of drugs that can isolate specific tumor characteristics, allowing for more effective treatment. But that is still years away.

Those early mammography trials were conducted before variations in cancer were recognized -- before Herceptin, before hormonal therapy, even before the widespread use of chemotherapy. Improved treatment has offset some of the advantage of screening, though how much remains contentious. There has been about a 25 percent drop in breast-cancer death rates since 1990, and some researchers argue that treatment -- not mammograms -- may be chiefly responsible for that decline. They point to a study of three pairs of European countries with similar health care services and levels of risk: In each pair, mammograms were introduced in one country 10 to 15 years earlier than in the other. Yet the mortality data are virtually identical. Mammography didn't seem to affect outcomes. In the United States, some researchers credit screening with a death-rate reduction of 15 percent -- which holds steady even when screening is reduced to every other year. Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice and co-author of last November's New England Journal of Medicine study of screening-induced overtreatment, estimates that only 3 to 13 percent of women whose cancer was detected by mammograms actually benefited from the test.

If Welch is right, the test helps between 4,000 and 18,000 women annually. Not an insignificant number, particularly if one of them is you, yet perhaps less than expected given the 138,000 whose cancer has been diagnosed each year through screening. Why didn't early detection work for more of them? Mammograms, it turns out, are not so great at detecting the most lethal forms of disease -- like triple negative -- at a treatable phase. Aggressive tumors progress too quickly, often cropping up between mammograms. Even catching them "early," while they are still small, can be too late: they have already metastasized. That may explain why there has been no decrease in the incidence of metastatic cancer since the introduction of screening.

At the other end of the spectrum, mammography readily finds tumors that could be equally treatable if found later by a woman or her doctor; it also finds those that are so slow-moving they might never metastasize. As improbable as it sounds, studies have suggested that about a quarter of screening-detected cancers might have gone away on their own. For an individual woman in her 50s, then, annual mammograms may catch breast cancer, but they reduce the risk of dying of the disease over the next 10 years by only .07 percent -- from .53 percent to .46 percent. Reductions for women in their 40s are even smaller, from .35 percent to .3 percent.

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.' "

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