SAN ANTONIO—In a population-based study comparing breast-conserving therapy with mastectomy, the former was associated with much improved overall survival and lower rates of regional recurrence and distant metastases. Included in the analysis reported at the San Antonio Breast Cancer Symposium were 37,207 patients in the Netherlands.
The rates of disease-free survival were similar, however, said the senior author, Sabine Siesling, PhD, Senior Researcher at the Netherlands Comprehensive Cancer Organization and Professor at the University of Twente in the Netherlands.
In the study (Abstract S3-05), she reported a 10-year overall survival rate of about 77 percent after breast-conserving surgery plus radiotherapy versus 60 percent for mastectomy (without radiotherapy). The 10-year disease-free survival rate was about 84 versus 81.5 percent, respectively.
Eliminating Residual Tumor Cells
“Although residual factors might explain part of the difference in recurrences, we hypothesize that radiation therapy might largely be responsible for better overall survival by eliminating residual tumor cells,” Siesling said at a news conference that highlighted the study.
Metastasis-free survival also differed between the study arms: Siesling said that additional analyses showed that patients with tumors up to 2 cm and no nodal involvement (T1N0) who received breast-conserving therapy had a significantly improved 10-year distant metastasis-free survival rate compared with those who received mastectomy.
Among all patients in the study, 11 percent had distant metastases after breast-conserving therapy compared with about 15 percent after mastectomy.
37,207 Dutch Women
Included in the study were 37,207 Dutch women diagnosed with early-stage breast cancer between 2000 and 2004: 21,734 patients (58.4 percent) received breast conserving therapy, and 15,473 patients (41.6 percent) received mastectomy.
Data from all 37,207 was used to estimate 10-year overall survival, and data from a subcohort of 7,552 patients with similar characteristics diagnosed in 2003 was used to estimate 10-year disease-free survival.
Siesling noted that the rates of local-regional recurrences did not differ significantly between the treatment groups: 2.1 percent of patients treated with breast-conserving therapy versus 4.0 percent of patients treated with mastectomy.
She explained that most observational studies showing that breast-conserving therapy confers better survival than mastectomy have been limited because they followed patients only for a maximum of five years, compared with 10 years in this trial.
Speculation about Radiation Therapy
“We think that radiation therapy may have played an important role in the difference in the outcomes from both treatments, although we cannot prove it with our data,” Siesling said. “We suggest that breast-conserving therapy should be the treatment of choice, especially in T1N0 stage breast cancer when it is medically feasible and according to the patient's wish.”
Siesling acknowledged that in this observational study, patients receiving breast-conserving therapy were younger and had more favorable tumor characteristics compared with patients receiving mastectomy. While these factors were corrected for in the multivariable analyses, they cannot be completely ruled out, she said.
The oral presentation was made by the study's first author, Marissa C. van Maaren, a junior researcher and doctoral student at the Netherlands Comprehensive Cancer Organization.
Van Maaren reported that patients receiving breast-cancer therapy were younger than the mastectomy patients, had smaller, well-differentiated, unifocal, or ductal tumors, had less hormonal therapy, and less axillary lymph node dissection.
She acknowledged that certain data were not available, including any adjuvant chemotherapy patients might have received, and that patients referred to mastectomy may have had more aggressive disease.
“There may have been selection biases and the differences we report may not be as large as we see here, but the differences were real,” van Maaren said.
Perspective from Carlos Arteaga
At the news conference, the moderator, Carlos L. Arteaga, MD, Co-Chair of the Symposium and Professor of Cancer Biology and Leader of the Breast Cancer Research Program at Vanderbilt-Ingram Cancer Center, was asked what impact these data might have on practice.
“I'm not sure it will change anything,” he said. “If anything, it reassures me that breast-conserving surgery is a good option for the patient who doesn't have a technical reason for removal of the whole breast—multicentricity, multifocality, or if the breast is too small for breast conservation to make any sense, or for the patient who has a germ line alteration that suggests that any breast tissue left is going to present a huge risk of having a second cancer.
“This is a retrospective study with a lot of data missing, such as what adjuvant treatment the patients might have received. In the absence of that, this study nonetheless reassures my belief that breast conservation in appropriately selected patients is the right thing to do.”