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New Canadian research has exposed the troubling reality that, for decades, we have probably been grossly overtreating early-stage breast cancer. In fact, ductal carcinoma in situ (DCIS) – a cluster of abnormal cells in the milk ducts – is probably not even cancer at all, though that's semantics.

So what are women, and people worried about cancer more generally, supposed to take from this?

First and foremost: This is progress. Painful, shocking, frustrating and confusing, perhaps, but progress nonetheless.

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Despite the fact that cancer is one of the top killers in Western society – there will be 78,000 cancer deaths in Canada alone this year, including 5,100 breast cancer deaths – we still have a lot to learn about the biology, the genetics, the risk factors and skillful detection and treatment (and non-treatment) of the multitude of diseases we lump under the catch-all term "cancer."

Breast cancer is fairly common: An estimated 25,200 cases will be diagnosed in Canada this year. About one-quarter of those cases, 6,000 or so, will be classified as DCIS, or stage 0 breast cancer. (There are five stages of cancer, from 0 to 4, based on the distance of spread from the point of origin, which is often a reflection of severity.)

The new study, led by Dr. Steven Narod of the Women's College Research Institute in Toronto, analyzed 20 years of data on 100,000 women diagnosed with DCIS.

It found that 3.3 per cent of DCIS patients died of breast cancer, regardless of their treatment – lumpectomy or mastectomy, with or without radiation. That is the same as the breast cancer mortality rate in the general population. This does not necessarily mean treatment was useless. But it does tell us that more aggressive treatment was not helpful and, in many cases, probably harmful.

Cancer is a word used to describe a malignant growth or tumour resulting from the abnormal division of abnormal cells. The notion that abnormal cells grow, spread out of control and become deadly has long been gospel, and this has led us to believe that the sooner we detect and treat cancerous cells the better.

But, in recent years, those fundamental beliefs have been challenged. The reality is that abnormal cells appear all the time in the body: Some multiply quickly and do harm, even deadly harm; some spread ever so slowly, meaning you die with cancer, not of cancer; and some cancers can even regress or disappear, with or without treatment. In other words, not all cancers metastasize and kill.

This has led to some new approaches to care, such as "watchful waiting" (also known as active surveillance) for men with prostate cancer. That means doing nothing – no surgery, no radiation, no chemotherapy – unless the cancer spreads.

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Could watchful waiting be the proper approach to DCIS? Perhaps, though we have to be clear that, while the new study suggests this, it does not demonstrate it.

As counterintuitive as it may seem, doing little or nothing, even when a "cancer" is detected, is a legitimate clinical choice, and it is not valued nearly enough.

As Dr. Otis Brawley, chief medical officer of the American Cancer Society, says: "Too often in medicine, we find something, we call it an illness and we overtreat it."

Before mammography, DCIS was virtually unknown, a condition seen only in autopsies. Advances in imaging technology have helped us see more – including lesions in milk ducts – but seeing does not necessarily mean understanding.

There was an assumption made that the clumps of abnormal cells dubbed DCIS were life-threatening and had to be treated aggressively. That assumption was wrong.

This should lead us to adjust treatment options, but also to some profound reflections, namely whether our population-wide screening programs are doing more good than harm.

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Too many of our policies – from screening to (over)treatment – are driven by fear, by the assumption that cancer is a savage killer that has to be hit early and hard.

In the past century, we have gotten a lot better at detecting cancer and preventing recurrences. But mortality rates remain stubbornly steady.

A key number in the new study bears repeating: Despite all our worries that breast cancer is a deadly scourge, only 3.3 per cent of women (about one in 29) will actually die of the condition.

That's still too many. What we need more than anything is better and more individualized treatments. That includes eliminating overtreatment.

We also need to keep this risk in perspective. Breast cancer is not a scythe hanging over every woman's head. Sometimes it's not even cancer at all. If anything, the new study should help dial down the fear.

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