The effect of radiation technique on survival was examined by comparing outcomes for patients receiving IMRT versus 3D CRT (Table 4). There were no differences between the groups for age at diagnosis, nor in the proportions of patients who received 50 Gy to the chest wall/breast, a dose to supraclavicular fossa (SCF), or a radiation boost. Survival analysis showed that radiation technique was not a significant factor for DFS (p=0.818) nor for OS (p=0.232) (Figure 2).
The effect of fractionation protocol on survival was examined by comparing outcomes for patients receiving conventional versus hypofractionated doses (Table 5). Patients receiving conventional fractionation were significantly younger (56.0 yr) than those receiving hypofractionation (62.7 yr; p=0.0001). However, there were no significant differences between the groups for DFS (p=0.678) or OS (p=0.395).
The effect of type of surgery on survival was examined by comparing outcomes for patients receiving breast-conserving surgery versus mastectomy (Table 6). There were no significant differences in age at diagnosis for the two surgery groups (p=0.409); however, better survival outcomes were evident for both DFS and OS in the conserved group (p<0.0001 and p=0.0015 respectively) (Figure 2). Reflecting these differences, T3 and T4 tumors were more common in the mastectomy group (p=0.001 and p=0.020 respectively) as were nodal status N1, N2 and N3 (p=0.007, p=0.0005 and p=0.0135 respectively). Significantly fewer mastectomy patients were categorized as T1 (p=0.001) and N0 (p<0.0001).
The effect of laterality on survival was examined in the patient cohort (Table 7). There were no significant differences in age at diagnosis for left versus right-sided tumors, nor in the radiation technique or fractionation protocols employed. However, irrespective of laterality, more patients were treated with hypofractionated doses than conventional protocols (p≤0.0002). There was no difference in OS (p=0.383) or DFS (p=0.057) for left versus right tumors.
The results of multivariate Cox proportional hazard modelling are summarized in Table 8. When all the factors are entered into the model, only tumor size T3/T4 and nodal status N2/N3 remained as significant factors for DFS (p=0.023 and p=0.0003 respectively). Tumor size (T3/T4) was the only significant factor for OS (p=0.019); nodal status – significant on univariate analysis –radiation technique (IMRT vs 3D CRT), fractionation protocol (conventional vs hypofractionated), surgery and chemotherapy were not significant factors for OS in the multivariate model (p>0.05; Table 8).