Or does it?

A recent study of mammography screening for breast cancer found that some invasive cancers might spontaneously regress over time, leaving no sign that they were ever present in a woman's body.

This leaves us to question if breast cancer is over diagnosed, and therefore over treated.

The research, conducted by Norwegian scientists, used 119,472 female subjects aged 50 to 64 years, who underwent three rounds of mammography (one mammogram every two years) from 1996 to 2001 as part of the Norwegian Breast Cancer Screening Program.

The cancer rates in this group were compared with the cancer rates of 109,784 control subjects who would have been screened if the program existed back in 1992. The control subjects were invited to have a one-time mammogram at the end of the observation period.

The team had expected that no matter when they were detected, the number of breast cancer tumors would ultimately be the same between the regularly screened group and the never screened controls.

As the researchers expected, the 4-year cumulative incidence of invasive breast cancer in the screened group was higher than in the non-screened control group - 1268 vs. 810 cases per one thousand women.

However, the surprise finding of the research was that even after the one time mammography was given to the previously unscreened control group, the six year cumulative incidence of breast cancer in the mammography screened group was still higher - 1909 vs. 1564 cases per one thousand women.

The study authors couldn't explain this.

There were no obvious differences between the two groups, and since that all important cumulative incidence of cancer in the control group never reached, even after one time screening, the mammography screened group of subjects, it lends support to the idea that some cancers found on repeat scans wouldn't show up on a single scan at the end of six years.

The study authors note, “This raises the possibility that the natural course of some screen-detected invasive breast cancers is to spontaneously regress.”

Perhaps as many as one in five cancers detected by mammogram might, in fact, spontaneously resolve.

And since two out of three breast cancer tumors are estrogen driven, the drop off of the hormone as women age and go through menopause suggests that cancer cells are naturally starved of the very hormone they need to grow and thrive.

The tumors might disappear altogether or shrink and lie dormant. The discontinuation of hormone replacement therapy (HRT) as a treatment for menopausal symptoms and the dramatic decrease in breast cancer rates lends fuel to the idea that hormones may fuel the growth of some cancers.

While this study is absolutely not a recommendation to skip your yearly mammogram, it does raise an intriguing question about cancers that may resolve themselves… without our ever knowing or treating them.

“If the spontaneous remission hypothesis is credible, it could cause a major reevaluation in the approach to breast cancer research and treatment,” says cancer expert Dr. Robert M. Kaplan of the University of California, Los Angeles, and Dr. Franz Porzsolt, from the University of Ulm, Germany in a related story that appeared with the study.

In effect, it could in the future lead to an approach that is already used for a well known cancer in men, prostate cancer, where a “Watchful Waiting” approach is sometimes advised.