Boost Radiation Reduces Ipsilateral Recurrence in Young Patients with Early Breast Cancer

Adding boost radiation to standard radiotherapy reduces the risk of recurrence in younger patients but has no impact on overall survival

medwireNews: Boost radiation after whole-breast radiation reduces the risk of ipsilateral recurrence in young patients after microscopically complete breast-conserving surgery, suggests research published in The Lancet Oncology.

After a median of 17.2 years of follow-up, 9% of the 2661 patients randomly assigned to receive a 16 Gy boost after 50 Gy radiation for stage I or II breast cancer experienced ipsilateral recurrence as a first treatment failure compared with 13% of the 2657 patients who received 50 Gy radiation alone, giving a hazard ratio of 0.65.

The 20-year cumulative incidence of ipsilateral breast cancer recurrence was 12.0% versus 16.4% in the boost and no boost groups, respectively, report Harry Bartelink, from The Netherlands Cancer Institute in Amsterdam, and co-authors.

However, there was a strong correlation between risk of ipsilateral recurrence and patient age, so that the 20-year cumulative risk ranged from 34.5% in patients aged 35 years or less to just 11.1% in patients aged over 60 years.

Thus, the reduction in risk of ipsilateral recurrence achieved by boost radiation was only significant in patients who were 40 years or younger and in those aged between 41 and 50 years.

And despite the reduced risk of ipsilateral recurrence, boost radiation did not significantly improve the 20-year rate of overall survival among patients compared with no boost (59.7 vs 61.1%), nor the cumulative risk of distant metastases (26.0 vs 24.8%).

While this may seem “contradictory”, the researchers attribute this pattern to “successful salvage mastectomy treatment for these breast recurrences”, as performed in 6.4% and 10.3% of the patients in the boost and no boost groups, respectively, within 10 years of radiation.

The team also cautions that boost radiation was associated with a significantly increased risk of developing fibrosis, with a 20-year cumulative incidence of 71.4% versus 57.2% with no boost. This included an increased cumulative incidence of severe fibrosis, at 5.2% versus 1.8%, although after stratifying by age, analysis showed this increased risk did not affect women aged less than 41 years.

Harry Bartelink et al therefore conclude: “A radiation boost after whole-breast irradiation has no effect on long-term overall survival, but can improve local control, with the largest absolute benefit in young patients, although it increases the risk of moderate to severe fibrosis.

“The extra radiation dose can be avoided in most patients older than age 60 years.”

Reference

Bartelink H, Maingon P, Poortmans P, et al. Whole-breast irradiation with or without a boost for patients treated with breast-conserving surgery for early breast cancer: 20-year follow-up of a randomised phase 3 trial. Lancet Oncol 2014; Advance online publication 9 December. doi:10.1016/S1470-2045(14)71156-8

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