When it comes to breast cancer, there are certain dogmas that we accept as fact:

First, a malignant tumor -- allowed to grow unchecked -- will eventually spread throughout the body and kill.

Second, regular mammograms are a must for women over 40 to find every mass before it turns deadly.

The trouble is, these "truths" aren't substantiated by scientific evidence. A new and somewhat shocking study out today shows that about 1 in 3 breast cancers detected on screening mammograms is overtreated. In other words, these malignancies wouldn't have caused symptoms or death in a woman's lifetime, according to research published in the British Medical Journal.

The study, reviewing data from women who began screening at age 50, specifically found that mammograms save 1 life for every 10 cancers that are diagnosed and treated unnecessarily. (Another study published three years ago measured 1 saved life for every 2 cancers unnecessarily treated.)

What this means is that mammograms lead to far more unnecessary surgeries and chemotherapy treatments than saved lives. "The real question is, how hard should we be looking for breast cancer?" asks Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Research who wrote an editorial that accompanied the study. That's a toughie because most women wouldn't feel comfortable knowing that they might have a potentially deadly breast tumor lurking in their body undetected. And, as breast surgeon Susan Love previously told me, doctors aren't able to discern the deadly cancers from the benign ones.

Welch thinks that women need to make informed decisions when it comes to deciding whether to be screened with mammograms, rather than being told simply that the X-ray is lifesaving. The new study showed some compelling evidence, graphing incidence rates of invasive breast cancer over the decades, beginning before screening was initiated. If mammography screening were working to find troublesome breast cancer in women in their 50s, then the incidence of breast cancer should have dropped for women who were screened in their 50s and 60s and who were now hitting their 70s when comparing them to those in their 70s who were never screened. Instead, the incidence rates don't drop below the rate that would be expected if women never had screening in the first place. What this suggests is that mammograms find a lot of tumors that may never have been found otherwise or caused any problems.

This is very similar to the dilemma posed by prostate cancer, says Welch.

Experts are now beginning to question the usefulness of PSA screening, given that autopsy studies show that invasive prostate cancer commonly occurs in men who die of something else.

On the other hand, women need to realize that there's simply no way to tell which invasive cancers will launch an all-out assault on their organs and which will stand idly by, doing no harm. The smart thing to do? Arm yourself with knowledge and determine what works best for you, which, as I wrote in my last blog post, breast cancer patients do all the time.

Welch drew up a nice balance sheet to show the upsides and downsides for every thousand women who undergo annual mammograms for 10 years.

On the plus side:

One woman out of 1,000 will avoid dying of breast cancer.

On the downside: Two to 10 women will be treated needlessly; 10 to 15 women will be told they have breast cancer earlier than they would have, though this won't affect their prognosis; 100 to 500 women will have at least one "false alarm" finding, and half of them will undergo a biopsy that turns out to be benign.

All doctors, Welch says, should discuss both the risks and benefits when counseling women on screening mammography.

"It's informed consent," he says. "I don't think a woman is crazy if she decides to have regular mammograms, but I also don't think she's crazy if she doesn't. It's the ultimate close call in medicine."

Breast Cancer: One Woman's Tough Treatment Decisions

This past spring, I spent several days at the University of Maryland Medical Center reporting on a piece about the art of medicine. It detailed how tough it is for doctors and patients to make medical decisions when the science is lacking to guide them. One patient I met was Miriam Smyth, a 51-year-old breast cancer patient from Gambrills, Md. She'd been diagnosed with a small breast tumor back in December and immediately decided to have a lumpectomy and radiation since her cancer had been caught early. But like so many other cancer patients, Smyth soon discovered that other treatment decisions aren't so easy to make.

Her first major dilemma -- whether or not to have chemotherapy -- was particularly difficult.

"I assumed I wouldn't need it, had even decided not to tell my young son or coworkers that I had cancer," Smyth tells me. Smyth, an oncology researcher at the University of Maryland Medical School, thought she'd have her surgery over Christmas break and head back to work without missing a beat. But then she had a test called Oncotype Dx, which revealed that her tumor had certain markers that put her at somewhat higher risk of having a recurrence. Suddenly, chemotherapy was back on the table.

"I read all the research on patients with similar Oncotype scores, but the data didn't help me," she says. "It was inconclusive as to whether I'd really be helped by the chemotherapy." Her husband, also a scientist, advised her to think about skipping the chemo, but she ultimately decided to have it. "I knew I'd never forgive myself if I had a recurrence," she explains. Still, it was tough for her emotionally. "I've studied these very same drugs in a lab, put them on human cells. I've seen the damage they do on a molecular level. But I had to get myself into the mind-set of being a patient and just deal with it."

After finishing the chemotherapy in May, Smyth had yet another decision to make: whether or not to start taking bone-building bisphosphonate drugs as part of a clinical trial being conducted at UMMC. The drugs might lower her risk of recurrence, but by how much? Smyth already had less than a 5 percent chance of having a relapse, thanks to all the treatments. Would slashing her risks an additional percentage point or two -- if that -- be worth the side effects? Her dentist told her she'd have to delay some planned dental work if she took the bisphosphonates because of the risks of a jawbone disease associated with these drugs.

Again, Smyth read the studies showing a lower risk of recurrence in breast cancer patients who took bisphosphonates. This time, however, she decided to skip the clinical trial. "I just wasn't convinced that the potential benefit, if any, outweighed the risks," she says. Smyth's case illustrated to me how personal these decisions really are for patients. When science can't firmly point the way to the right decision, women have to go with their gut and ask themselves, what's really right for me?

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