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The breast cancer drug trastuzumab (better known by its brand name Herceptin) has had more than its share of good press. It has been described as "the biggest cancer breakthrough in a decade," "a life-saving drug" and the "next best thing to a cure."

The laudatory words from some oncologists and patient advocates, along with extensive media coverage, have placed enormous pressure on public health plans to fund the treatment. Much of the debate has focused on the price Genentech Inc. is asking for Herceptin -- between $35,000 and $45,000, depending on the patient's weight.

Providing Herceptin to a select group of breast cancer patients would effectively double the cost of treatment and add $150-million a year to the health-care tab.

But that's a small price to pay for a miracle, right?

Let's leave the discussion of pricing for another day and focus instead on the other numbers, the ones that tell us just how effective Herceptin can be in ridding women of breast cancer. (Before going any further, let's remember that Herceptin is designed only for breast cancer sufferers who produce too much HER-2 protein -- about one in four cases.)

The most eye-popping claim is that, for this select group, the drug cuts the risk of recurrence by half. In clinical trials, women who took Herceptin along with a standard chemotherapy drug saw their risk of recurrence fall 52 per cent, compared to women who received chemo alone. That is an impressive relative risk reduction.

But what matters in the real world is absolute (not relative) risk reduction. Practically speaking, 15 per cent of women taking Herceptin and chemo had a recurrence of breast cancer within four years of diagnosis, compared to 33 per cent of women who took chemo alone. That is an absolute risk reduction of 18 per cent.

Nobody wants a recurrence, but what matters ultimately is survival. Herceptin, according to the studies, cut the death rate by one-third. That sounds impressive, but relative risk reductions always do. In reality, the difference in the death rate between the Herceptin and non-Herceptin groups was 2 per cent after three years, and 4 per cent after four years.

Based on those numbers, can we honestly say that Herceptin is an essential lifesaving drug?

Like every drug, Herceptin has side effects. In the clinical trials, the rate of heart failure was 3 per cent higher among women receiving Herceptin. Is trading breast cancer for heart failure the next best thing to a cure?

When it comes to drugs, miracles are often short-lived. Tamoxifen was once the next best thing to a cure for postmenopausal women with breast cancer. Despite early promise, follow-up studies showed that after five years of use, the drug actually increased the risk of recurrence, along with increasing the risk of endometrial cancer.

Then along came letrozole (a drug taken after five years of tamoxifen), which in studies also cut the risk of recurrence by half. The jury is still out on whether the medication will increase the risk of cardiovascular disease.

But at least physicians and women prescribed the earlier drugs have access to the full data. The most troubling aspect of the Herceptin story is how little evidence of its effectiveness has been published in peer-reviewed medical journals.

Clinical trials testing Herceptin for treatment of early-stage breast cancer were cut short in April after an interim analysis showed "better than expected" results. Halting research early is controversial at the best of times. When it has been done in the past -- most famously in the study declaring hormone replacement therapy to increase the risk of breast cancer, heart attacks and stroke -- the data were published immediately.

The Herceptin data have been presented selectively at scientific conferences, in press releases and news reports. That's bad science. It's also pretty flimsy evidence on which to make declarations of miracles, and on which to base tens of millions of dollars in spending.

Women are being advised to take this treatment, and provincial health plans forced to make decisions on funding, based on inadequate data.

Perhaps it's not fair to single out Herceptin. Every pharma company dreams of this kind of buzz for its drug. But it is, in the words of Herceptin's promoters themselves, the dawning of a new era where we will target disease at its genetic roots, with costly new drugs.

This requires a new era of rigorous, dispassionate analysis that provides health professionals and patients with timely data on effectiveness and cost-effectiveness of all drugs.

Herceptin has not met this test.

In the months and years to come, there will be many vaunted pharmaceutical miracles, many next-best-things-to-a-cure. They must be kept in perspective. We cannot, in our desperate desire for good news, suspend our critical faculties.

When it comes to Herceptin, some healthy skepticism is, well, quite healthy.

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