Mammograms Leading To Breast Cancer Overdiagnosis: Study

The findings of new research suggest that mammograms may not be the life saving breast cancer diagnosis tool that the public believes, indicating that mammograms often lead to the overdiagnosis of breast cancer, which may result in unnecessary side effects or death. 

In a study published last week in the New England Journal of Medicine, researchers found that four times as many tumors that are not dangerous or fatal are misdiagnosed because of the wide spread use of mammograms.

Researchers focused on data from two time periods, before widespread mammograms were implemented and after. Data was taken from the Surveillance, Epidemiology, and End Results (SEER) program from 1975 through 2012 for women over the age of 40. The first study period was 1975 to 1979 and 2000 to 2002 after widespread mammography was implemented.

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Study data indicated the proportion of small breast tumors detected increased from 36% to 68%. The tumors that were found were small, measuring less than 2 cm. The proportion of large tumors detected decreased from 64% to 32%. These were large tumors measuring greater than 2 cm.

Overall, researchers detected 162 more cases of breast cancer diagnosed per 100,000 women after implementing widespread mammography. They noted only 30 of the 162 small tumors found per 100,000 women were expected to progress to become large.

Study authors said the data suggests the remaining cases were breast cancer misdiagnosis, detecting tumors that would never have led to clinical symptoms or death. The study indicates four times as many cancer cases were over diagnosed  because of widespread mammography.

“Women were more likely to have breast cancer that was over diagnosed than to have easier detection of a tumor that was destined to become large,” wrote study authors.

Doctors often attribute the reduction in breast cancer deaths to early detection from mammograms, but the findings of the new study suggest the two-thirds reduction in breast cancer deaths is from improved treatment.

Mammograms Standard Practice

Mammograms use x-ray technology to take a picture of breast tissue to check for cancer in women who have no symptoms of the disease. They can also be used to screen a woman’s breast tissue after a lump has been discovered. In some cases, mammograms can offer false-positive results indicating the presence of cancer, when no cancer is actually occurring.

Another goal of mammography is to detect small tumors before they grow into large tumors that can cause symptoms. The aim is not to find the most cancers, but to find cancers that are significant and dangerous to women’s health.

The American Cancer Society guidelines call for women to consider having a mammogram at age 40, then to have one every year beginning at age 45. By age 55, they recommend women should have one every other year. Other medical associations have similar recommendations.

Researchers say the new study will not change mammogram guidelines, as the goal is to detect cancer early, but the data shows a trend that should be examined. Doctors and  researchers recommend if a woman finds a breast lump they should have a mammogram immediately.

The problem that researchers are now focusing on is how to treat nonthreatening tumors that are found, as not all are deadly. There are other options and technologies that may not pose a threat to women.

Other health groups say the overall incidence of breast cancer is increasing, but the results of this study assume the incidence is not.

“This trend was less the result of a substantial decrease in the incidence of large tumors and more the result of a substantial increase in the detection of small tumors,” wrote study authors.

Breast cancer is the most common cancer in women. More than 240,000 women are diagnosed with breast cancer every year, resulting in nearly 41,000 deaths. Breast cancer affects about 1 in 8 women. Rates began to decrease in 2000, after seeing dramatic increases in the previous two decades.


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