Survival and recurrence rates in Australians with HER2-positive early breast cancer are “reassuringly” comparable to those reported in landmark clinical trials despite only two-thirds of patients completing the standard 12-month course of trastuzumab (Herceptin), new real-world data reveals.

The observational study of almost 15,000 HER2-positive early breast cancer patients who received adjuvant trastuzumab between 2007 and 2016 found overall survival (OS) rates at five years were 92.7%.

According to the authors, led by Dr Monica Tang from the Centre for Big Data Research in Health at the University of NSW, this figure compared favourably with the 4-year OS rate of 89.3% see in the HERA trial and five-year OS rates of 91–92% reported in the BCIRG 006 trial.

A nine-year survival rate of 87.9% seen in the trial was also similar to the 10-year OS (84%) reported in the NCCTG N98931/NSABP B-31 trials.

Furthermore, recurrence free survival (RFS) rates seen in the study at five and nine years were 86.8 and 81.4%, respectively.

“These figures may underestimate true recurrence rates as they are based on the receipt of trastuzumab for metastatic disease as a surrogate for recurrence … however, they are not dissimilar to 4-year DFS rates of 78.6–85.3% and 5-year DFS rates of 81–84% reported in clinical trials,” the research team noted in their paper published in the British Journal of Cancer.

Results also revealed that patients who failed to complete 12 months of therapy with trastuzumab had a 41% increased risk of death compared with those who did (HR 1.41, 95% CI 1.23–1.62) after adjusting for risk factors for non-completion such as age and socioeconomic disadvantage.

However, while noting that the absolute difference between the groups was small (nine-year OS rate 86.2 vs. 90.2%) the authors said a lower than expected rate of trastuzumab completion in routine practice had implications for the real-world applicability and assessment for reimbursement of novel HER2-targeted agents.

They added that the study illustrated the differences between RCT populations and patients treated in clinical practice and highlighted the value of real-world studies in verifying and complementing clinical trial findings.