Sunday, July 13, 2014

Treating precancers reduces breast cancer deaths

Breast cancer deaths rose through the '70s and '80s, but declined in the '90s. For nearly the past 20 years, American women have had about a 2% annual drop in the breast cancer death rate.

Here is the mortality graph provided by the National Cancer Institutes SEER (Surveillance, Epidemiology and End Results) program.

Though nobody wants to take the blame for the rise in breast cancer deaths in the '70s and '80s, lots of people want credit for the fall of breast cancer deaths that began in the '90s. Was it due to a reduction to the exposure of carcinogens, or to better treatment, or to earlier diagnosis?

The fall in breast cancer deaths does not seem to be due to cancer prevention. While the deaths from breast cancer were falling, there was an apparent rise in the incidence of breast cancer cases. Here is the SEER graph for the incidence in breast cancer in the U.S.

Since the breast cancer incidence rose while the deaths from breast cancer dropped, it seemed as though the benefit must have come from better treatment or earlier detection.

A major study, attempting to resolve this issue, was published in the New England Journal of Medicine, in 2005:

Effect of screening and adjuvant therapy on mortality from breast cancer.
Berry DA, Cronin KA, Plevritis SK, Fryback DG, Clarke L, Zelen M, Mandelblatt JS, Yakovlev AY, Habbema JD, Feuer EJ; Cancer Intervention and Surveillance Modeling Network (CISNET) Collaborators. N Engl J Med 353:1784-1792, 2005.

They concluded that that 28 to 65 percent of the sharp decrease in breast cancer
deaths from 1990 to 2000 was due to mammograms. The remainder of the improvement was was attributed improved breast cancer treatment.

The study did not take into account the great contribution of precancer treatment to the reduction of breast cancer deaths.

Let's review this SEER data, this time taking into account the diagnosis of DCIS (ductal carcinoma in situ) a precancer that precedes the development of invasive breast cancer. Here is the SEER data for the incidence of all breast cancer and of DCIS (the precancer for breast cancer).

In the past few decades, there has been a huge rise in the number of diagnosed cases of breast precancers. This is due largely to the use of mammography, which can detect lesions that cannot be found by palpation. When a precancer is detected and removed, the patient does not develop invasive cancer.

The total number of breast cancer cases includes cases of DCIS. If we subtract the number of breast precancer cases (DCIS) from the total number of breast cancer cases, we get the incidence of invasive breast cancer cases. Here is the SEER data.

The middle bars in the graph represent the incidence of invasive breast cancers. The graph shows that incidence of invasive breast cancers has actually dropped since the early '90s, as the diagnosis and treatment of DCIS has risen.

Much of the decrease in breast cancer mortality can be accounted for by the diagnosis and treatment of breast precancers. In fact the drop in breast cancer deaths follows the same slope, and has about the same magnitude, as the drop in invasive breast cancers that follows the increase in breast precancer treatments.

- © 2010 Jules Berman

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