Treatment with lumpectomy and radiotherapy was associated with a significant reduction in breast cancer mortality in patients with ductal carcinoma in situ (DCIS), compared with a lumpectomy alone or a mastectomy alone, investigators reported in JAMA Oncology.
Among women who received adjuvant radiation, there was an associated 23% reduced risk of dying of breast cancer. This extrapolated to a cumulative mortality of 2.33% for those treated with lumpectomy alone and 1.74% for women treated with lumpectomy and radiotherapy at 15 years (adjusted hazard ratio, 0.77; 95% confidence interval, 0.67-0.88; P less than .001).
“Although the clinical benefit is small, it is intriguing that radiotherapy has this effect, which appears to be attributable to systemic activity rather than local control,” wrote Vasily Giannakeas, MPH, of the Women’s College Research Institute, Toronto, and colleagues.
Emerging evidence suggests that adding radiotherapy to breast conserving surgery can reduce the risk of breast cancer mortality among women with DCIS and lower the risk of local recurrence. Because of the low rate of mortality associated with DCIS, the authors noted that it has been difficult to investigate deaths related to DCIS. The association of adjuvant radiotherapy with breast cancer survival in this population has also not yet been clearly established.
To determine the extent to which radiotherapy is associated with reduced risk of breast cancer mortality in patients treated for DCIS and identify patient subgroups who might derive the most benefit from radiotherapy, the authors conducted a historical cohort study using the Surveillance, Epidemiology, and End Results database. A total of 140,366 women diagnosed with first primary DCIS between 1998 and 2014 were identified, and three separate comparisons were made using 1:1 matching: lumpectomy with radiation versus lumpectomy alone, lumpectomy alone versus mastectomy, and lumpectomy with radiation therapy versus mastectomy.
A total of 35,070 women (25.0%) were treated with lumpectomy alone, 65,301 (46.5%) were treated with lumpectomy and radiotherapy, and 39,995 (28.5%) were treated with mastectomy.
The overall cumulative mortality for the entire cohort from breast cancer at 15 years was 2.03%. The actuarial 15-year mortality rate for the mastectomy group (2.26%) was similar to those who had lumpectomy without radiotherapy (2.33%).
The adjusted HR for death for mastectomy versus lumpectomy alone (based on 20,832 propensity-matched pairs) was 0.91 (95% CI, 0.78-1.05). The adjusted hazard ratios for death were 0.77 (95% CI, 0.67-0.88) for lumpectomy and radiotherapy versus lumpectomy alone (29,465 propensity-matched pairs), 0.91 (95% CI, 0.78-1.05) for mastectomy alone versus lumpectomy alone (20,832 propensity-matched pairs), and 0.75 (95% CI, 0.65-0.87) for lumpectomy and radiotherapy versus mastectomy (29,865 propensity-matched pairs).
When looking at subgroups and the effect of radiotherapy on mortality, the authors found the following: The HR was 0.59 (95% CI, 0.43-0.80) for patients aged younger than 50 years and 0.86 (95% CI, 0.73- 1.01) for those aged 50 years and older; it was 0.67 (95% CI, 0.51-0.87) for patients with ER-positive cancers, 0.50 (95% CI, 0.32-0.78) for ER-negative cancers, and 0.93 (95% CI, 0.77-1.13) for those with unknown ER status.
“How exactly radiotherapy affects survival is an important question that should be explored in future studies,” the authors concluded.
There was no outside funding source reported. Mr. Giannakeas is supported by the Canadian Institutes of Health Research Frederick Banting and Charles Best Doctoral Research Award.
SOURCE: Giannakeas V et al. JAMA Network Open. 2018 Aug 10. doi:10.1001/jamanetworkopen.2018.1100.