The Impact of Boost Dose and Margins on the Local Recurrence Rate in Breast Conserving Therapy: Results From the EORTC Boost-No Boost Trial
Breast conserving therapy (BCT) consists of a breast conserving surgery (i.e. a lumpectomy) followed by radiation therapy. BCT is considered a standard treatment option for early stage breast cancer patients, as it permits organ preservation while achieving similar long-term survival as mastectomy. However, BCT is associated with a risk of local breast cancer recurrence or a second cancer in the same breast, ranging from 0.5-2.5% per year.
Currently, patients are treated with radiation to the whole breast, followed by a "boost". The boost is an extra dose of radiation to the area where the tumor was located. This study was designed to see if the boost was a necessary part of the treatment plan.
The study enrolled over 5,300 patients and the median * follow up time for this data was 10.8 years. The rate of an in-breast tumor recurrence (IBTR) was 7% in the patients who had the boost versus 12% in those who did not get the boost. The decrease in IBTR was seen in all age groups, but was most impressive in women under 40 years old (their rate was 23.9% vs. 13.5%).
Overall, those at highest risk for IBTR were patients under 50, those with high grade tumors and those with DCIS and positive margins. Interestingly, invasive breast cancer with positive margins was not found to be high risk. This study supports the current use of a boost to the tumor bed to decrease the risk of IBTR. It is assumed that this will also improve overall survival, but that question was not a part of this study design.
* The median is the "middle of the pack", where half of the patients have had more than the median number of years since treatment, and half have had less than the median. For instance, if the patients were 2, 4, 6, 10.8, 12, 12 and 14 years since treatment, 10.8 is the mid point, or the median. It is different from the mean, which would be the average time since treatment.
Partially funded by an unrestricted educational grant from Bristol-Myers Squibb.