Comparison of treatment outcome between invasive lobular and ductal carcinomas in patients receiving partial breast irradiation with intraoperative electrons
Menée à partir de données portant sur 2 173 patientes atteintes d'un carcinome lobulaire invasif ou d'un carcinome canalaire invasif traité par chirurgie conservatrice entre 1999 et 2007, cette étude compare, du point de vue des taux de récidive à 5 et 10 ans et en fonction des caractéristiques de la tumeur (type, sous-type moléculaire, taille) et de catégories d'âge, l'efficacité d'une irradiation partielle accélérée du sein à l'aide d'une radiothérapie intra-opératoire par faisceaux d'électrons
Purpose : To investigate the local outcome of patients after accelerated partial breast irradiation (APBI) with intraoperative electrons (IORT) for invasive lobular carcinoma (ILC) compared to invasive ductal carcinoma (IDC). Materials and methods : From 1999 to 2007, 2173 patients were treated with breast conserving surgery and IORT (21Gy /1 fraction) as the sole local treatment: 252 patients with ILC (11.6%) were compared to 1921 patients with IDC in terms of local control. Results : Compared to the IDC subgroup, patients with ILC had a low-risk profile and were more hormone-responsive. The 5- and 10-year in-breast tumor reappearance (IBTR) rate was 5.5% and 14.4% for the IDC group and 7.5% and 21.8% for the ILC group (log-rank p=0.03).The excess risk of IBTR associated with ILC was particularly high for small tumors (≤1cm: HR=2.24; 95% CI 1.03-4.85), elderly patients (60-69 years: HR=2.27; 95% CI 1.11-4.63; ≥70 years: HR=3.28; 95% CI 1.08-10.0), low grade tumors (grade 1: HR=3.50; 95% CI 1.05-11.7) and Luminal A molecular subtype (HR=3.18; 95% CI 1.49-6.77). Of the ILC histological variants, no difference between classic and non-classic subgroups was observed, although the signet ring cell and solid variants had the worst local control. Conclusions : In spite of a favorable tumor profile, APBI with IORT led to a higher incidence of IBTRs in patients with ILC compared to those with IDC. Our institutional experience emphasized the importance of the size of the irradiation field, pointing to the use of larger collimators, even when dealing with small tumors, to improve local control.