Increased overall survival independent of RECIST response in metastatic breast cancer patients continuing trastuzumab treatment: Evidence from a retrospective study

Recent studies have reported the potential clinical utility for metastatic breast cancer (MBC) patients of continuing trastuzumab beyond progression. Based on those results, here the authors have examined the benefits of trastuzumab-continuation by specifically evaluating RECIST responses upon first line trastuzumab-treatment as a potential predictive marker for therapeutic effect of trastuzumab-continuation beyond metastatic disease progression. The authors carried out a retrospective analysis of 272 HER2 positive MBC patients under trastuzumab treatment at 22 different oncology Italian centers during the years of 2000 and 2001 who progressed under first line trastuzumab-treatment. The primary end point of the study was the survival from the date of first documented progression upon first line trastuzumab treatment of disease. Data analysis involved the use of matching on propensity score to balance variables between treated and untreated subjects and to reduce bias. Of the 272 HER2-positive MBC patients, 154 (56.6%) continued treatment. 79 (51.3%) of those 154 patients showed responses based on RECIST criteria during first-line trastuzumab-treatment. Of the 118 patients that suspended trastuzumab, RECIST responses had been observed in 44 (37.3%). Cox proportional hazards analysis of progressed patients, matched using propensity score, showed that discontinuation of trastuzumab at metastatic disease progression was a risk factor for significantly reduced overall survival in both responder (HR = 2.23; 95% CI = 1.03-4.82) and non-responder groups (HR = 3.53, 95% CI = 1.73-7.21), with no significant differences in the two estimated HRs (P-value of the likelihood-ratio test = 0.690). Continued trastuzumab treatment after disease progression has clinically and statistically significant effects in both RECIST responder and non-responder MBC patients.