Their study, presented at the San Antonio Breast Cancer Symposium, could change the way breast cancer is treated in the future. Now, patients routinely receive chemotherapy as their first treatment, followed by surgery. Patients with estrogen-positive tumors --tumors that use estrogen to fuel their growth -- may then receive endocrine therapies that block the estrogen action or production, or interfere with the hormonal pathways.
This study suggests patients with estrogen-positive cancer may benefit more from an initial treatment of endocrine therapies rather than chemotherapy.
"We hope this study will help to direct the best treatment for patients," says the study's author, Aman Buzdar, M.D., professor in the Department of Breast Medical Oncology at M. D. Anderson. "In the future, we may be able to identify patients who will do well with endocrine therapies alone."
Buzdar and a team of researchers looked at tumor samples of 1,018 patients followed at the center since 1975 in which the estrogen receptor status was known. All patients received chemotherapy and surgery.
The investigators looked for the evidence of a complete "pathological response" to treatment (there was no invasive cancer left either in the breast or in the lymph nodes), and separated the results by estrogen receptor status. They found that more than 20 percent of patients with estrogen-negative breast cancer had a complete pathologic response compared with five percent in estrogen-positive cancer.
"It didn't matter what kind of chemotherapy was used, there was more benefit observed in patients with estrogen receptor-negative cancers," says Buzdar. "Even though a significant number of estrogen-positive patients had clinical regression in their tumors, there was not the same numbers of pathological complete response."
Buzdar says that because these two breast cancer subtypes behave in dissimilar ways, they also respond differently to chemotherapy treatment. "Estrogen negative cancers are more poorly differentiated and tend to be more sensitive to chemotherapy drugs, and are easier to kill with chemotherapy," he says. "Estrogen receptor-positive breast cancers are differentiated and tend to be less responsive to chemotherapy.
"These results support what has been suspected. Breast cancer patients with estrogen receptor-positive disease may have better likelihood of response to endocrine therapies but the role of chemotherapy in this set of patients needs to be further defined," continues Buzdar. "In the future, we may be able to tell which patients should receive chemotherapy, which should have endocrine treatments, and which might benefit from both."