Ischemic Cardiac Events Following Treatment of the Internal Mammary Nodal Region Using Contemporary Radiation Planning Techniques
Menée à partir de données portant sur 2 126 patientes atteintes d'un cancer du sein traité entre 1984 et 2007 (durée médiane de suivi : 9,3 ans), cette étude évalue l'association entre une irradiation de la chaîne mammaire interne et la survenue d'événements cardiaques ischémiques
Purpose : Regional nodal irradiation, including radiation (RT) to the internal mammary nodal (IMN) region, improves oncologic outcomes in node-positive breast cancer patients. Concern remains, however, given the proximity of the IMN to the heart and the association between cardiac RT exposure and toxicity. The objective of the study was to evaluate rates of ischemic cardiac events (ICEs) and associated risk with the treatment of the IMN region. Methods and Materials : The cardiac outcomes of 2,126 patients treated with adjuvant breast or breast and nodal RT from 1984-2007 at a single institution were reviewed. The primary endpoint was an ICE following RT initiation. The association between IMN-RT and ICEs was assessed using Cox proportional hazards models. Both IMN-RT and three-dimensional conformal radiotherapy (3DCRT) began in 1997, therefore 3DCRT-only subset analyses were performed to minimize bias associated with improved treatment technique. Results : Median follow-up was 9.3 years. Eighty-seven patients (4.1%) experienced an ICE. No increased 10-year rate of ICEs was observed with IMN-RT compared to no IMN-RT in the total cohort (3.2% [95%CI:2.4-4.3] versus 3.4% [95% CI:1.5-7.5], respectively, Hazard Ratio (HR)=0.88, p=0.73). Similarly, no statistically significant difference was noted in the 3DCRT-planned, left-sided disease subset (5.1% [95%CI:1.8-14.1] versus 4.0% [95%CI:2.0-8.0] respectively; HR=1.18, p=0.76). In multivariable-analysis, adjusting for cardiac risk-factor imbalances, no significant increased hazard was noted with IMN-RT (HR=1.84, p=0.28) in the 3DCRT-planned, left-sided disease subset. Conclusions : No statistically significant association between IMN-RT and ICEs was demonstrated in a review of patients treated at a single institution from 1984-2007. Given the long natural history and low overall rate of ICEs, continued follow-up of the present study and additional studies in the 3DCRT-era are warranted to confirm these results. Minimizing cardiac exposure, when treating a limited IMN field, is critical to limit excess risk of ICEs.