Impact of radiation therapy modalities on loco-regional control in inflammatory breast cancer

Introduction In inflammatory breast cancer (IBC), radiotherapy intensification is considered a standard of care by some teams, although the level of evidence remains low. We sought to analyze the impact of radiotherapy modalities on the risk of loco-regional and distant relapse. Methods A retrospective multicenter study included patients with localized IBC treated between 2010 and 2017. Standard post-mastectomy radiotherapy consisted of daily fractions to a total dose of 50 Gy equivalent without a boost or bolus, while intensified radiotherapy referred to the use of a boost or bolus. The cumulative incidence curves of loco-regional and distant recurrence were displayed using the competing risk method. Results Of the 241 included patients, 165 were treated with standard and 76 with intensified radiotherapy. There was significantly more nodal involvement in the intensified group. With a median follow-up of 40 months post-radiotherapy, there was no difference between standard vs intensified radiotherapy regarding the cumulative incidence of loco-regional (p=0.68) or distant recurrence (p=0.29). At 5 years, the risks of loco-regional and distant recurrence were 12.1% (95% CI, 7.5; 17.7) and 29.4% (95% CI, 21.8; 37.3) for patients treated with standard radiotherapy and 10.4% (95% CI, 4.4; 19.3) and 21.4% (95% CI, 12.6; 31.9) for intensified radiotherapy. On multivariate analyses, triple-negative subtype and absence of complete pathological response (pCR) were associated with a higher risk of loco-regional recurrence. Radiotherapy intensification had no significant impact on loco-regional and distant recurrence. For non-pCR patients (n=172, 71.7%), no significant differences were observed between the two groups for loco-regional (p=0.80) and distant recurrence either (p=0.39). Severe toxicity rates were similar in both groups. Conclusions Contrary to other important series, this large retrospective multicentric study did not show a loco-regional or distant control benefit of intensified radiotherapy. Pooled prospective studies and meta-analyses of intensified radiotherapy are warranted to endorse this approach.