Mammography & breast cancer: sometimes what you see is not what you get.
The study took advantage of the Norwegian commitment to health care for all and excellent record-keeping. Norway introduced mammography screening in 1996 and, since then, almost every woman aged 50-64 has taken part in the screening program. The study looked at the difference in the numbers of cancers found over six years in women who were screened every two years starting at age 50 versus the number found in women who were about five years older when screening started and were only screened once (for the study). The researchers assumed that the women only screened once would have slightly fewer cancers detected, because a single screening mammogram always misses a few cancers. They were surprised when the cancer registry data showed that many fewer cancers were detected in the women screened once in their mid-50s compared to those who were screened three times between age 50 and 56. Screening regularly resulted in the diagnosis of 191 breast cancers in every 10,000 women screened, while screening once found only 156 cases of breast cancer in 10,000 women.
What to make of this? The researchers believe that the most likely explanation is that some cancers go away on their own with no treatment. (2) Strange as it seems, the medical literature is full of reports of various types of cancers that were diagnosed, and then disappeared without any treatment. No one is sure why or how this happens--maybe the person's immune system is somehow able to attack and kill the cancer cells, or maybe the cancerous tumor isn't able to stimulate the formation of enough new blood vessels to support itself. But, until now, reports of such spontaneous regression were oddities, thought to happen only rarely. This is the first study that makes it seem as if cancer disappears more frequently.
Does this mean that women who are diagnosed with breast cancer found via screening mammography can safely ignore their cancer and assume that it will 8o away on its own? No! Unfortunately, no one has any way to tell which cancers will regress in this way. What this study does mean is that we now know a little more than we did before about why the use of screening mammograms hasn't reduced breast cancer deaths as much as was hoped. For more information about NWHN's current position on screening mammography, see NWHN's Mammography Fact Sheet, available at: http://www. nwhn.org/healthinfo/options/print.cfm?info_id=20.
(1) Zahl P, Maehlen J, and Welch G, "The Natural History of Invasive Breast Cancers Detected by Screening Mammography," Archives of Internal Medicine 2008; 168(21):2311-2316.
(2) Papac RJ, "Spontaneous regression of cancer," Cancer Treatment Reviews 1996; 22(6): 395-428.
Cindy Pearson is the NWHN's Executive Director
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|Publication:||Women's Health Activist|
|Date:||Jul 1, 2009|
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