Background: The CHER-LOB randomized phase II study showed that the combination of lapatinib and trastuzumab plus chemotherapy increases the pathologic complete response (pCR) rate compared with chemotherapy plus either trastuzumab or lapatinib. Here we report the results of survival analysis according to treatment arm and pCR. Methods: The CherLOB study randomized 121 HER2-positive, stage II-IIIA breast cancer patients to anthracyclines/taxane-based chemotherapy plus trastuzumab, lapatinib, or both. After surgery, patients received adjuvant trastuzumab for up to 1 year. The primary end point of the study was met, with a relative increase of 80% in the pCR rate achieved with chemotherapy plus trastuzumab and lapatinib compared with chemotherapy plus either trastuzumab or lapatinib (Guarneri, J Clin Oncol 2012). Relapse-free survival (RFS) was calculated from randomization to breast cancer recurrence (locoregional or distant) or death from any cause, whichever first. Overall survival (OS) was calculated from randomization to death from any cause. Results: At a median follow up of 8.8 years, RFS rates at 5 years were: 85.8% in the trastuzumab + lapatinib arm, 77.8% in the trastuzumab arm, 78.1% in the lapatinib arm (log-rank p = 0.160). Patients treated with dual HER2 blockade (trastuzumab + lapatinib arm) experienced numerically better RFS as compared to patients treated with single HER2 blockade (trastuzumab arm and lapatinib arm combined): 5-yr RFS 85.8% vs 78.0%, log-rank p = 0.087; HR = 0.51, 95% CI 0.23-1.12, p = 0.093. The achievement of pCR was a strong prognostic factor. 5-yr RFS rate was 97.3% for pCR patients vs 72.9% for non-pCR patients (log-rank p < 0.001, HR = 0.12, 95% CI 0.03-0.49, p = 0.003); similar significant results were observed in both the estrogen receptor-negative and estrogen-receptor positive subgroups. OS was also improved in pCR patients: 8-yr OS rates were 97.2% vs 80.0% for non pCR patients (log-rank p = 0.028, HR = 0.14, 95% CI 0.02-1.08, p = 0.060). Conclusions: In the Cher-LOB study, there was a not statistically significant signal for a better RFS for patients who received dual HER2 blockade with trastuzumab and lapatinib plus chemotherapy as compared to patients treated with single anti-HER2 agent (trastuzumab or lapatinib) plus chemotherapy. Patients achieving a pCR had longer RFS and OS as compared to non-pCR patients. Clinical trial information: NCT00429299.