Radiotherapy after mastectomy for women with one to three positive nodes significantly reduces the risk of recurrence and breast cancer mortality, researchers found in a meta-analysis.
With follow-up of 20 years for breast cancer mortality, a review of 22 randomized trials found that among women with one to three positive nodes after mastectomy and axillary dissection, radiotherapy reduced the rates of overall recurrence by almost a third (relative risk, 0.68; 95% confidence interval, 0.57-0.82; P = .00006) and breast cancer mortality by a fifth (RR, 0.80; 95% CI, 0.67-0.95; P = .01), investigators reported online March 19 in the Lancet.
This benefit from radiotherapy in women with one to three positive nodes held up when women also received chemotherapy and/or hormone treatment. The proportional reductions in the rates of any first recurrence and breast cancer mortality did not differ significantly according to whether or not systemic therapy was given, the investigators said.
The group analyzed outcomes for 8,135 women enrolled in 22 studies, randomized to receive radiotherapy to the chest wall and regional lymph nodes after mastectomy and axillary surgery, or to receive the same surgery with no radiotherapy. The median length of follow-up per woman was about 9 years, although many in the studies have now been followed for up to 20 years. Most had positive nodes at dissection (72%); 20% had node-negative disease, and nodal status was unknown for the remainder.
For women with no positive nodes, radiotherapy had no significant effect on locoregional recurrence, overall recurrence, or breast cancer morality, but did however increase overall mortality (RR, 1.23; 95% CI, 1.02-1.49; P = .03). For women with axillary dissection and four or more positive nodes, radiotherapy reduced overall recurrence (RR, 0.79; 95% CI, 0.69-0.90; P = .0003) and breast cancer mortality (RR, 0.87; 95% CI, 0.77-0.99; P = .04).
All of the studies were conducted between 1964 and 1986. Benefits could be even greater today, "... because radiotherapy planning has changed substantially and women today receive better coverage of target areas. Furthermore, doses to normal tissues are lower today, so the risks of radiotherapy are also likely to be lower," wrote the investigators with the Early Breast Cancer Trialists’ Collaborative Group, which conducted the analysis (Lancet 2014 March 19 [doi: 10.1016/S0140-6736(14)60488-8]).
"Breast cancer is a disease with a long natural history," the researchers wrote. "Many of the women in these trials have now been followed up for 20 years and therefore they provide information about the long-term benefits of radiotherapy. Radiotherapy techniques have improved in the past few decades, and so the proportional benefits of radiotherapy are likely to be larger than in these trials."
However, they added, "the absolute risks of breast cancer recurrence and mortality have [been] reduced in many countries because of advances in detection and treatment of breast cancer, so the absolute benefits from postmastectomy radiotherapy today are likely to be smaller than those reported here."
The study group is funded by Cancer Research UK, the British Heart Foundation, and the UK Medical Research Council. None of the members reported any financial disclosures.