Washington ? Women examining their breasts are unable to detect tumors early enough to reduce their risk of dying from breast cancer, suggests a decadelong study of more than 260,000 women in Shanghai, China.

Dr. David Thomas, lead author of the study, said women should not stop examining their breasts but should have realistic expectations about the value of the exams.

“She’s got to do a very good job, and she’s got to realize it is unproven,” he said, adding that self-exams should not be a substitute for mammography.

The finding was the latest in the confusing, often contradictory information women have been given over the past year related to breast cancer and early detection. A study earlier this year questioned the value of mammograms in detecting breast cancers and saving lives.

Thomas said the latest study, appearing today in the Journal of the National Cancer Institute, raises questions about the time and expense it takes to teach breast self-examination to women, especially those in developing countries. His conclusion is based on a decadelong effort to teach factory workers in Shanghai the proper way of doing breast self-examination and to determine whether the effort made a difference in the rate of cancer deaths.

“In spite of the fact that we spend all of this time and effort in teaching breast self-exam, the women were not able to detect lumps early enough to make a difference,” Thomas said.

In poorer countries, where mammography is not routinely available, Thomas said the study suggests that public health officials should not spend their limited money on teaching self-examination but on other programs, such as immunizations.

In the United States, where mammography is common, doctors should not emphasize breast self-examination, he said.

Other experts, however, said the study will not affect their continuing recommendation that women perform self-examinations between their regular routine breast screening tests.

“It remains important for women to be familiar with their own anatomy, and certainly teaching signs and symptoms of cancer is of value,” said Dr. Benjamin Anderson, a breast surgeon and the clinical medical director of the Breast Care and Cancer Research Program at the University of Washington. “We will continue to recommend monthly self-examination as part of routine breast health care. We will not be abandoning that aspect.”