Better Survival With Breast-Conserving Therapy for Early-Stage Breast Cancer

Sabine Siesling, PhD

Women with early-stage breast cancer treated with breast-conserving therapy had significantly improved 10-year overall survival compared with women who underwent mastectomy without radiation therapy, according to the results of a population-based study (abstract S3-05) presented at the 2015 San Antonio Breast Cancer Symposium (SABCS).

In addition, the study found that breast-conserving therapy resulted in an improved distant metastasis-free survival compared with mastectomy in patients with T1, N0 breast cancer.

“The overall survival for breast-conserving therapy compared to mastectomy is better in every T and N stage,” said Sabine Siesling, PhD, senior research at the Netherlands Comprehensive Cancer Organisation, Utrecht, and professor at the University of Twente, Enschede, during a press conference. “Breast-conserving therapy should be the treatment of choice especially in smaller tumors.”

According to Siesling, previous trials have shown that breast-conserving therapy and mastectomy have similar rates of overall survival in women with early-stage breast cancer and some observational studies have shown that breast-conserving therapy may confer an improved overall survival.

“Most of these observational studies only followed patients for a maximum of 5 years. Since recurrences are described to occur after 5 years as well, getting more insight into the long-term outcomes after different type of surgery based on daily practice experience on a national level is of great importance,” Siesling said in a prepared statement.

In this study, the researchers looked at two cohorts of Dutch patients treated between 2000 and 2004 to determine if there was a difference in 10-year overall survival and distant metastasis-free survival when treated with breast-conserving therapy compared with mastectomy.

The first cohort looked at overall survival in 37,207 patients. Of these patients, 58.4% were treated with breast-conserving therapy. According to Siesling, these patients were younger and had smaller, well-differentiated, unifocal, ductal tumors.

The study found that patients assigned to breast-conserving therapy had a better overall survival than patients treated with mastectomy. After adjusting for confounding factors, there was a hazard ratio [HR] of 0.81 (95% confidence interval [CI], 0.78–0.85; P < .001) in favor of better survival for patients who underwent breast-conserving therapy compared with mastectomy. According to Siesling, these results were similar in all the subgroups examined.

The second cohort of 7,552 patients looked at 10-year distant-metastasis free survival in a subgroup diagnosed in 2003 who had active follow-up registering all recurrent events within 10 years. In this group, 61.5% of patients had breast-conserving therapy and 38.5% had mastectomy. Distant metastasis occurred in 11% of the breast-conserving therapy patients and 14.7% of the mastectomy patients.

After correction for confounding variables, the difference in 10-year distant metastasis–free survival was not significantly different for the two groups (HR, 0.88 [95% CI, 0.77–1.01]; P = .070). However, when the researchers looked at patients with T1, N0 disease there was a significant improvement in 10-year distant metastasis–free survival in favor of breast-conserving therapy (HR, 0.74 [95% CI, 0.58–0.94]; P = .014).

Siesling cautioned that observational studies are prone to confounding by indication. In this study, patients receiving breast-conserving therapy were younger and had more favorable tumor characteristics compared to patients receiving mastectomy. “We corrected for all of these factors in the multivariable analyses; however, we cannot completely rule out this phenomenon,” she said. “In addition, residual confounding caused by non-measured factors could also have altered the results. However, we do not expect these factors to overrule the large impact of all variables we included in the analyses.”