[Role of locoregional radiation therapy in breast cancer patients with negative lymph nodes after preoperative chemotherapy and mastectomy. The Institut Curie-Hôpital René-Huguenin experience]

Purpose: Neoadjuvant chemotherapy generally induces significant changes in the pathological extent of disease and challenges the standard indications of adjuvant postmastectomy radiation therapy. We retrospectively evaluated the impact of postmastectomy radiation therapy in breast cancer patients with negative lymph nodes (pN0) after neoadjuvant chemotherapy.

Patients and materials: Among 1054 breast cancer patients treated with neoadjuvant chemotherapy in our institution between 1990 and 2004, 134 patients had pN0 status after neoadjuvant chemotherapy and mastectomy. Demographic data, tumor characteristics, metastatic sites, and treatments were prospectively recorded. The impact of postmastectomy radiation therapy on locoregional recurrence-free survival and overall survival was evaluated by multivariate analysis including known prognostic factors.

Results: Among 134 eligible patients, 78 patients (58.2%) received postmastectomy radiation therapy, and 56 patients (41.8%) did not. With a median follow-up time of 91.4 months, the 10-year locoregional recurrence-free survival and overall survival rates were 96.2% and 77.2% with postmastectomy radiation therapy and 86.8% and 87.7% without radiation therapy, respectively (no significant difference). In multivariate analysis, there was a trend towards poorer overall survival among patients who did not have a pathologically complete primary tumour response after neoadjuvant chemotherapy (hazard ratio [HR], 6.65; 95% CI, 0.82-54.12; P=0.076). Postmastectomy radiation therapy had no effect on either locoregional recurrence-free survival (HR, 0.37; 95% CI, 0.09-1.61; P=0.18) or overall survival (HR, 2.06; 95% CI, 0.71-6; P=0.18). There was a trend towards poorer overall survival among patients who did not have pathologically complete in-breast tumour response after neoadjuvant chemotherapy (HR, 6.65; 95% CI, 0.82-54.12; P=0.076).

Conclusions: This retrospective study showed no increase in the risk of distant metastasis, locoregional recurrence or death when postmastectomy radiation therapy was omitted in breast cancer patients with pN0 status after neoadjuvant chemotherapy and mastectomy. Whether the omission of postmastectomy radiation therapy is acceptable for these patients should be addressed prospectively.