Premenopausal women who have been diagnosed with breast cancer may want to think twice before opting for surgery, according to a study published last week by Harvard Medical School (HMS) researchers.

According to the study, which appeared in the International Journal of Surgery, 20 percent of women with cancer that had spread to the lymph nodes experienced a relapse within the first 10 months after surgery.

“We noticed that there was a early relapse peak, and also a late relapse peak,” said lead scientist Michael W. Retsky, who is a lecturer in surgery at the Children’s Hospital and HMS. “Our analysis showed that the second peak was caused by the natural course of the disease. The first peak, however, was too sharp to be explained by natural phenomena—we postulated that it was stimulated by surgery.”

Retsky said that this surgery-induced relapse could accelerate disease progression by two years and cause an increase of one death per 10,000 women diagnosed with breast cancer.

According to the latest estimates published by the American Cancer Society, over 200,000 new breast cancer cases will be diagnosed this year, and over 40,000 will die from the disease.

Retsky said his research was inspired by the “mammography paradox.”

“Researchers were looking for the benefits of early diagnosis in breast cancer, and expectedly, there was an advantage for women over 50,” he said. “However, there was an disadvantage for women 40 to 49 years old.”

Women in that age group who were diagnosed with breast cancer early died sooner than women who opted not to receive mammograms.

But Retsky emphasized that his findings do not mean that women should bypass surgery as a form of therapy.

“If you look at the long-term trends, early detection of cancer combined with surgery still has a high rate of cures for small cancers—pre or post-menopausal,” he said. “We are definitely not recommending any change in clinical practice.”

Daniel B. Kopans, professor of radiology at Massachusetts General Hospital and HMS, said current methods of early screening and treatment for women have led to reduced mortality rates and should not be changed without further evidence.

Researchers hypothesize that the unexpected proliferation of other tumors after the excision of a primary tumor during surgery may result because the primary tumors actually suppress distant growths.

Retsky said that such a system would be favored by evolution because the primary tumor would allow women to live for a few more years—time enough to bear more offspring. Removal of such primary tumors would cause growth of other tumors, thereby triggering a relapse of the cancer.

Retsky noted that these hypotheses have yet to be confirmed scientifically. However, he said future research may be able to pinpoint the specific mechanism responsible for post-surgical cancer relapse, which in turn may open the door to additional therapies for breast cancer.

—Staff writer Risheng Xu may be reached at xu4@fas.harvard.edu.