WEDNESDAY, Oct. 6, 2004 (HealthDayNews) -- Women who are obese when they are diagnosed with early stage breast cancer are at greater risk of dying from the disease than patients considered normal weight, a new study finds.
Even after adjusting for such risk factors as age and menopausal status, "obesity still came out as a significant independent predictor for worse outcomes," said Dr. Penny Anderson, lead author of the study and a radiation oncologist at Fox Chase Cancer Center in Philadelphia.
Five-year survival rates for normal weight and overweight women averaged 92 percent for each group of women, vs. 88 percent for women defined as obese. The five-year rate of distant metastasis, when cancer spreads to other parts of the body, was 7 percent for patients with normal weights, 6 percent for overweight women, and 10 percent for obese individuals.
The study, presented Oct. 6 at the American Society for Therapeutic Radiology and Oncology's annual meeting in Atlanta, helps to confirm a link between obesity and breast cancer survival. Previous studies have reported contradictory results about the influence of obesity on survival rates.
It's also among the first study to explore obesity's negative influence on outcomes in early-stage breast cancer, when the disease is generally believed to be most treatable.
Researchers at Kaiser Permanente of Southern California observed a similar connection between body weight and breast-cancer death in a study reported in the September 2004 issue of the Archives of Surgery. Women with early stage breast cancer in the heaviest weight group had a nearly 2.5-fold increased risk of dying from the disease compared to women in the lightest weight group.
Breast cancer is the most common cancer in women, excluding skin cancer, and the second leading cause of cancer-related death in women, after lung cancer, according to the American Cancer Society. In 2004, an estimated 217,440 women in the United States will be diagnosed with the disease and roughly 40,580 women will die from it.
In the study, researchers relied on data from 2,010 patients who underwent treatment from 1978 to 2003 for "stage I/II" breast cancer. Doctors use "staging" to determine the amount of cancer in the body and its location. That information is useful in planning the course of treatment and determining a patient's prognosis.
At stage I, a tumor is less than 2 centimeters and has not spread to the lymph nodes. Stage II tumors range from 2 to 5 centimeters and may have spread to the lymph nodes in the underarm area. Tumors larger than 5 centimeters also may be considered stage II if there is no lymph node involvement, according to the American Joint Committee on Cancer.
The women in the study received a breast-conserving lumpectomy, lymph node removal and radiation therapy. They may or may not have been treated with chemotherapy.
Researchers grouped the women into categories based on their body mass index, a ratio of height to weight. At diagnosis, 22 percent of the patients (452 women) were normal weight, 43 percent (857 women) were overweight and 35 percent (701 women) were obese.
Obese women tended to be older and postmenopausal, the study found. But there were no statistical differences among the three weight groups in tumor size or number of lymph nodes involved.
"These women were not presenting with bigger tumors," Anderson said, referring to patients in the obese group.
Obesity was not found to be a significant predictor of a recurrence of cancer in the treated breast. But it did put women in the study at greater risk for developing metastatic disease and dying of their cancer.
As the prevalence of obesity and the risk for breast cancer each increases with age, it's important for women to manage their weight throughout their life, Anderson said.
"Enhanced weight control can certainly help improve someone's outcome," she said.
The American Cancer Society has more about the risk factors for breast cancer.