Breast-conserving therapy (lumpectomy plus radiation therapy) appears to improve 10-year overall survival for women with early breast cancer compared with mastectomy, according to a very large population-based study from the Netherlands.1 However, the study raises more questions than it answers, according to many experts.
Ten-year overall survival was 76.8% with breast-conserving therapy vs 59.7% with mastectomy—a difference that was highly statistically significant (P < .001).
“Our study found improved 10-year overall survival for breast-conserving therapy for every tumor and nodal stage. We saw improved 10-year distant metastasis–free survival for breast-conserving therapy only in T1 N0 stage but no difference between the two surgical techniques for [distant metastasis–free survival] for other stages,” said Marissa van Maaren, MD, of the Netherlands Comprehensive Cancer Organization in Utrecht, who presented the findings at the 2015 San Antonio Breast Cancer Symposium.
The study had several limitations, she acknowledged, including imbalances in baseline characteristics favoring the breast-conserving therapy group and no information on microscopic activity, comorbidities, or HER2 status.
“Over the years, randomized controlled trials have shown similar survival for breast-conserving therapy and mastectomy for stages T1-2 N01 breast cancer. Recent studies suggest improved survival for breast-conserving therapy, but these studies only had 5-year follow-up,” stated Dr. van Maaren. “We wanted to extend the follow-up for at least 10 years and also wanted to look at 10-year distant metastasis–free survival.”
Study Details and Results
The study included 37,207 women diagnosed with a primary breast tumor between 2000 and 2004 entered in the Netherlands Cancer Registry. They included tumors up to 5 cm with no more than three positive nodes treated with either breast-conserving therapy or mastectomy. Patients with macroscopic residual disease and those who had neoadjuvant therapy were excluded.
Ten-year overall survival was calculated for a cohort diagnosed between 2000 and 2004. Ten-year distant metastasis–free survival was calculated in a cohort diagnosed in 2003.
Comparing Surgical Techniques in Early Breast Cancer
- A large population-based study found that overall survival was improved by breast-conserving therapy with lumpectomy and radiation therapy vs mastectomy alone in women with early breast cancer.
- In general, younger women with more favorable tumor characteristics underwent breast-conserving therapy, which may have influenced the findings.
- Unmeasured confounding factors call the findings into question and caution against changing current practice based on these study results.
Breast-conserving therapy was used by 58.4% of the entire sample—generally in younger women and in those with more favorable tumor characteristics (ductal, unifocal disease, less hormonal therapy, and less maxillary lymph node dissection).
“At a median follow-up of 11.2 years, after correcting for confounding factors, breast-conserving therapy reduced the risk of death by 21% compared with mastectomy,” said Dr. van Maaren. “This was true for every TNM stage.”
At a median follow-up of 9.8 years to the first distant metastasis, distant metastasis was reported in 11% of the breast-conserving therapy group vs 14.7% of the mastectomy group (total in cohort, 7,552 patients). This difference was not statistically significant, except for the T1 N0 subgroup, who benefitted from breast-conserving therapy vs mastectomy.
Questions From the Audience
Several audience members at Dr. van Maaren’s presentation took issue with the study, questioning whether all patients had the same axillary staging, sentinel node testing, radiotherapy, and other treatments. Also, questioners said that the breast-conserving therapy group received radiation therapy and more hormonal therapy, whereas the mastectomy group did not receive radiation therapy. Furthermore, some audience members pointed out that the results mirror the selection criteria for breast-conserving therapy—younger age, smaller well-differentiated tumors, for example. ■
Disclosure: Dr. van Maaren and coauthors reported no potential conflicts of interest.
Reference
1. van Maaren MC, de Munck L, de Bock GH, et al: Higher 10-year overall survival after breast conserving therapy compared to mastectomy in early stage breast cancer: A population-based study with 37,207 patients. 2015 San Antonio Breast Cancer Symposium. Abstract S3-05. Presented December 10, 2015.
