Distribution of Locoregional Breast Cancer Recurrence in Relation to Postoperative Radiation Fields and Biological Subtypes.

PURPOSE: To investigate incidence and location of locoregional recurrence (LRR) in patients who have received postoperative locoregional radiation therapy (LRRT) for primary breast cancer. LRR-position in relation to applied radiotherapy and the primary tumor biological subtype were analyzed with the aim of evaluating current target guidelines and radiation therapy techniques in relation to tumor biology. METHODS AND MATERIALS: Medical records were reviewed for all patients who received postoperative LRRT for primary breast cancer in southwestern Sweden from 2004 to 2008 (N = 923). Patients with LRR as a first event were identified (n = 57; distant failure and death were considered competing risks). Computed tomographic images identifying LRR were used to compare LRR locations with postoperative LRRT fields. LRR risk and distribution were then related to the primary breast cancer biologic subtype and to current target guidelines. RESULTS: Cumulative LRR incidence after 10 years was 7.1% (95% confidence interval [CI], 5.5-9.1). Fifty-seven of the 923 patients in the cohort developed LRR (30 local recurrences and 30 regional recurrences, of which 3 cases were simultaneous local and regional recurrence). Most cases of LRR developed fully (56%) or partially (26%) within postoperatively irradiated areas. The most common location for out-of-field regional recurrence was cranial to radiation therapy fields in the supraclavicular fossa. Patients with an estrogen receptor negative (ER-) (hazard ratio [HR], 4.6; P < .001; 95% CI, 2.5-8.4) or HER2+ (HR, 2.4; P = .007; 95% CI, 1.3-4.7) primary breast cancer presented higher risks of LRR compared with those with ER+ tumors. ER-/HER2+ tumors more frequently recurred in-field (68%) rather than marginally or out-of-field (32%). In addition, 75% of in-field recurrences derived from an ER- or HER+ tumor, compared with 45% of marginal or out-of-field recurrences. A complete pathologic response in the axilla after neoadjuvant treatment was associated with a lower degree of LRR risk (P = .022). CONCLUSIONS: Incidence and location of LRR seem to be related to the primary breast cancer biologic subtype. Individualized LRRT according to tumor biology may be applied to improve outcomes.