TUESDAY, Aug. 16, 2005 (HealthDay News) -- Women whose breast cancer is detected by a screening mammogram have a better prognosis than those whose cancer is found symptomatically, even if the cancer has spread to the lymph nodes, a new study suggests.
"Everyone knows finding cancer mammographically gives you longer survival due to lead time," said senior study author Donald A. Berry, chairman of the department of biostatistics and applied mathematics at the University of Texas M.D. Anderson Cancer Center.
Lead time refers to the time between when the tumor is detected by mammography and when the tumor would have been detected in the absence of screening -- such as finding the lump by feeling it. Mammogram-detected tumors, Berry said, "tend to be found sooner than those found symptomatically," he said.
What is new in this study, he said, is that the researchers considered women with the same characteristics, including age, tumor size and involvement of the lymph nodes, and found there is still an advantage with finding the cancer by mammogram vs. other detection methods, he said.
"It's the second paper to report this," Berry said. "One other Finnish study reported this, too."
The new study appears in the Aug. 17 issue of the Journal of the National Cancer Institute.
For the study, Berry's team evaluated data from three large randomized breast cancer screening trials. They included the Health Insurance Plan of New York, which assigned 62,000 women to screening or a control group, and two Canadian studies that evaluated nearly 45,000 women who were screened and nearly the same number in control groups who were not.
The researchers then focused on the women in the studies who were eventually diagnosed with breast cancer. They compensated for the stage of cancer to eliminate "lead-time bias" and found women whose cancers were discovered after a previous negative mammogram (by methods other than a mammogram) had a 53 percent higher risk of death than those whose cancer was detected by the regular screening mammograms. Those in the control group (in which no mammogram was used) had a 36 percent higher risk of breast cancer death compared to those who were screened by mammograms.
The difference in survival is due to a "length bias," because screening detects more slow-growing tumors, Berry said.
Dr. Herman Kattlove, medical editor for the American Cancer Society in Los Angeles, said the study findings are of interest to researchers and women alike. "A woman who is screened every year and finds a lump in between [screenings] has a different cancer than one whose cancer is detected on a mammogram," he said.
"They may be biologically different cancers, and probably more aggressive," he said. "The message for women is, continue getting mammograms. It still will save lives."
Women should also know that if they find a lump between mammograms, it is crucial to see a doctor as soon as possible, Kattlove said, because the cancer may be more aggressive.
Added Berry: "The message is not that screening is good or screening is bad. We didn't address that question. But there is a distinct survival advantage if women get mammograms."
"A woman who has had her tumor detected mammographically can breathe an extra sigh of relief because her tumor is, on average, less lethal than her sister's tumors detected symptomatically," he said.
More information
For more on breast cancer, visit the American Cancer Society.
