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Trying to Understand the Real Numbers

Posted 8/19/2015

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  Today we are back to statistics. Any discussion of statistics related to cancer must begin with the obvious statement that for any one person, the possible outcome is either 100% or 0% bad--meaning that any one person's cancer will either recur or it won't, and there is no way to absolutely predict what the future will bring. Over the past few weeks, I have been especially reminded of this as I have been meeting with two women whose breast cancer recurred almost twenty years after their initial diagnosis and treatment.

  The number commonly used is that approximately 30% of all women who are diagnosed with early breast cancer (defined as breast cancer that has not spread beyond the breast and axilla) will eventually have a recurrence of their disease. The plot thickens when we learn that this number has been thrown around for years based on a couple of not so great studies. It thickens more when we learn that the estimate was rounded up because those studies included only women with Stage I and Stage II cancer; some women with Stage III breast cancer also fit the definition above.

  Not to keep you in suspense, it turns out that the 30% is probably accurate. But now there is a basis for it--sadly, the real number did not turn out to be better than we had hoped. Given all the conversation about advances in breast cancer treatment, especially for women with her2 positive disease, one would have assumed this would be better. It's not.

FFrom Medscape comes this essay by Nick Mulchaey. Here is the start and a link:

The Mystery of a Common Breast Cancer Statistic -- Solved

A commonly cited breast cancer statistic — that 30% of all early-stage breast cancers will progress, despite treatment, to deadly metastatic disease — appears to have no strong contemporary evidence to back it up.
Nonetheless, the statistic appears widely. For example, it is cited in an academic report (J Intern Med. 2013;274:113-126), in a breast cancer charity report, in a pharmaceutical marketing piece, and on a major cancer center website. In short, the 30% figure is conventional wisdom — despite the absence of an authoritative epidemiologic source.
But is that statistic accurate and reflective of current clinical reality? And should clinicians repeat it to patients? Perhaps more importantly, does the statistic really matter? After all, the treatment of women with early-stage disease will not change whatever the statistic is, correct?
Medscape Medical News went in search of answers to these questions and found angry patients, a clinician author trusted blindly by a lot of people, and special access to a common database that, in fact, appears to solve the mystery of the proportion of early-stage patients who progress to metastatic disease.
Our story begins with multiple women with metastatic breast cancer who are dismayed or angry about the fuzziness and mystery of the 30% statistic, and have said so online.

http://www.medscape.com/viewarticle/849644_print

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