(CNN) - Surgery is tied to improved chances of survival among stage 4 breast cancer patients, a new study suggests, but who has access to surgery and who doesn't can vary drastically, based on factors including income level and where treatment is administered.
Surgery to remove tumors was associated with a 44% increased chance of survival within an average followup period of 21 months, according to the abstract, to be presented at the American Association for Cancer Research's annual meeting in Atlanta this week.
"If breast surgery is to be considered by patients and providers when deciding treatment strategy, it will be imperative to address significant disparities among patients who are offered surgical therapy," the researchers wrote.
The study involved data on 3,231 women with HER2-positive stage 4 breast cancer, which tests positive for higher levels of a protein called HER2. The data came from the National Cancer Database between 2010 and 2012.
The data showed that most women, 89.4%, were treated with chemotherapy or immunotherapy; 37.7% underwent endocrine therapy; and 31.8% underwent radiation. Overall, 35%, or 1,130 women, underwent surgery; the rest did not.
Surgery was more likely to be performed in patients with private insurance or Medicare than in those who were uninsured or on Medicaid; those in the lowest income quartile compared with the highest; and those who received other treatments, said Dr. Sharon Lum, a professor and medical director of the Breast Health Center and Loma Linda University in California, who was senior author of the study.
"Surgery was less likely to be performed in older patients compared with younger; non-Hispanic black patients compared with white; those treated at an academic or research facility compared with community programs; and those with larger tumor size," she said.
The study also analyzed where surgery fits in with other treatment options available to patients, such as targeted medications, said Ross Mudgway, a medical student at the University of California, Riverside School of Medicine, who was first author of the study.
The findings suggest that surgery to remove a breast tumor still should be considered in addition to standard targeted medications and other therapies if a woman has stage 4 HER2-positive breast cancer.
"We hope that our results encourage clinicians to consider surgical treatment in the face of metastatic disease while weighing the risks and potential benefits in this particular subset of patients who have new, effective targeted therapy options," Mudgway said.
The study had some limitations, including that there was only an association found between surgery and survival, and the data did not include specific information on which other targeted therapies were used among the patients.
Additionally, "we do not yet have randomized controlled trial results that address the impact of surgical removal of the breast tumor in patients with HER2-positive metastatic breast cancer," Lum said.
"So using observational data from the large NCDB dataset can help address the questions about surgical treatment that providers and patients are asking today," she said.
Traditionally, surgery has been a standard part of treating breast cancer, along with drugs and radiation.
Yet in stage 4 metastatic breast cancer, "it doesn't make much sense to cut out the cancer in the breast if there is cancer in other parts of the body," said Dr. Monica Morrow, a surgical oncologist and chief of breast service in the Department of Surgery at Memorial Sloan Kettering Cancer Center in New York, who was not involved in the study.
"The patients who had surgery were the ones who had better responses to chemotherapy, probably had less metastatic disease and were probably healthier," she said. "So maybe they lived longer because of surgery, or maybe they would have lived longer anyway, and the study shows that doctors know how to identify patients who will do well."
In other words, more research is needed to determine whether those factors are influencing the new study's findings, since databases -- like the one used in the new study -- can sometimes suffer from selection bias.
"The question of a benefit for surgery can only be answered by a prospective randomized trial," Morrow said.
She added that another researcher in the field, Dr. Seema Khan, a professor of cancer research at Northwestern University's Feinberg School of Medicine, has been leading such a trial.
"We eagerly await the results," Morrow said.
Dr. Tari King, chief of breast surgery at the Dana-Farber/Brigham and Women's Cancer Center in Boston, called the new study "interesting" but cautioned that the findings should not be over-interpreted since "there are many biases" related to why some patients may or may not be selected for surgery, she said.
For instance, patients with a good response to first-line or initial therapy would have been selected for subsequent surgery, "whereas those whose disease was refractory to first-line therapy would have not been offered surgery. Therefore, stacking the cards in favor of the surgery group," King said.
"The risks and benefits of local therapy -- surgery plus radiation -- for breast cancer are favorable when surgery is being performed for curative intent," she said.
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