Some breast cancers may naturally regress: study

The American Cancer Society estimated that about 465,000 women die of breast cancer globally each year, and 1.3 million new cases are diagnosed.

"I think generally when we look at studies like this it is important to keep in mind there are some studies that change practice and others that make us think a little bit more, said Dr. Eric Winer, director of the Breast Oncology Center at Dana-Farber Cancer Institute in Boston.

"The idea that somehow these cancers go away entirely is, I would say, an intriguing hypothesis, but one we don't have a lot of evidence to support," said Winer, who was speaking on behalf of the American Society of Clinical Oncology.

In much of Europe women undergo mammograms every two years after age 50 except for in Britain where it is every three years, Zahl said. The American Cancer Society recommends that women get an annual mammogram beginning at age 40.

Bob Smith, director of cancer screening for the American Cancer Society, said Zahl's team misinterpreted the data, and expressed doubt about the idea that a significant number of breast tumors "spontaneously regress."

"I imagine there are still some people who believe the Earth is flat, but there are not very many of them," Smith said in a telephone interview. "It's not usual -- it happens every day that research is published that gets it wrong."

The researchers acknowledged many doctors might be skeptical of the idea but they cited 32 reported cases of a breast cancer regressing, a small number for such a common disease.

The researchers said their findings provide new insight on what is "arguably the major harm associated with mammographic screening, namely, the detection and treatment of cancers that would otherwise regress."

(additional reporting by Julie Steenhuysen; Editing by Will Dunham and Angus MacSwan)