By Elaine Schattner, MD|April 3rd, 2012
This week’s stir comes from the Annals of Internal Medicine. In a new analysis, researchers applied complex models to cancer screening and BC case data in Norway. They estimated how many women found to have invasive breast cancer are “overdiagnosed.” I cannot fathom why the editors of the Annals gave platform to such a convoluted and misleading medical report as Overdiagnosis of Invasive Breast Cancer Due to Mammography Screening: Results From the Norwegian Screening Program. But they did.
Here are a few of my concerns:
1. None of the four authors is an oncologist.
2. The researchers use mathematical arguments so complex to prove a point that Einstein would certainly, 100%, without a doubt, take issue with their model and proof.
3. “Overdiagnosis” is not defined in any clinical sense (such as the finding of a tumor in a woman that’s benign and doesn’t need treatment). Here, from the paper’s abstract:
The percentage of overdiagnosis was calculated by accounting for the expected decrease in incidence following cessation of screening after age 69 years (approach 1) and by comparing incidence in the current screening group with incidence among women 2 and 5 years older in the historical screening groups, accounting for average lead time (approach 2).
No joke: this is how “overdiagnosis” – the primary outcome of the study, is explained. After reading the paper in its entirety three times, I cannot find any better definition of overdiagnosis within the full text. Based on these manipulations, the researchers “find” an estimated rate of overdiagnosis attributable to mammography between 18 -25% by one method (model/approach 1) or 15-20% (model/approach 2).
4. The study includes a significant cohort of women between the ages of 70-79. Indolent tumors are more common in older women who, also, are more likely to die of other causes by virtue of their age. The analysis does not include women younger than 50 in its constructs.
5. My biggest concern is how this paper was broadcast – which, firstly, was too much.
Bloomberg News takes away this simple message in a headline: “Breast Cancer Screening May Overdiagnose by Up to 25%.” Or, from the Boston Globe’s Daily Dose, “Mammograms may overdiagnose up to 1 in 4 breast cancers, Harvard study finds.” (Did they all get the same memo?)
The Washington Post’s Checkup offers some details: “Through complicated calculations, the researchers determined that between 15 percent and 25 percent of those diagnoses fell into the category of overdiagnosis — the detection of tumors that would have done no harm had they gone undetected.” But then the Post blows it with this commentary, a few paragraphs down:
The problem is that nobody yet knows how to predict which cancers can be left untreated and which will prove fatal if untreated. So for now the only viable approach is to regard all breast cancers as potentially fatal and treat them with surgery, radiation, chemotherapy or a combination of approaches, none of them pleasant options…
This is simply not true. Any pathologist or oncologist or breast cancer surgeon worth his or her education could tell you that not all breast cancers are the same. There’s a spectrum of disease. Some cases warrant more treatment than others, and some merit distinct forms of treatment, like Herceptin, or estrogen modulators, surgery alone…Very few forms of invasive breast cancer warrant no treatment unless the patient is so old that she is likely to die first of another condition, or the patient prefers to die of the disease. When and if they do arise, slow-growing subtypes should be evident to any well-trained, modern pathologist.
“Mammograms Spot Cancers That May Not Be Dangerous,” said WebMD, yesterday. This is feel-good news, and largely wishful.
A dangerous message, IMO.
Addendum, 4/15/12: The abstract of the Annals paper includes a definition of “overdiagnosis” that is absent in the body of the report: “…defined as the percentage of cases of cancer that would not have become clinically apparent in a woman’s lifetime without screening…” I acknowledge this is helpful, in understanding the study’s purpose. But this explanation does not clarify the study’s findings, which are abstract. The paper does not count or otherwise directly measure any clinical cases in which women’s tumors either didn’t grow or waned. It’s just a calculation. – ES