Survival and cardiac toxicity in patients with HER2‐positive, metastatic breast cancer treated with trastuzumab in routine clinical practice

AIMS: We sought to describe survival outcomes and toxicities of trastuzumab in real-world patients with HER2-positive, metastatic breast cancer (MBC) and compare these to a recent systematic review of clinical trials. METHODS: We searched the medical records of three Sydney cancer centers for patients with HER2-positive, MBC starting trastuzumab from January 2001 to March 2017. We recorded patient, tumor, and treatment characteristics; survival times from start of palliative trastuzumab; and rates of cardiac toxicity. Survival distribution was summarized using the following percentiles (represented scenario): 90th (worst-case), 75th (lower-typical), 25th (upper-typical), and 10th (best-case). Survival times were compared to recent review of HER2-positive MBC randomized trials. Factors associated with survival were assessed with Cox models. RESULTS: Characteristics of the 126 patients were: median age 53 years, ER positive cancer (50%), de-novo metastatic disease (23%), prior adjuvant trastuzumab (15%), liver metastases (37%), and brain metastases (23%). The median duration of first-line trastuzumab was 11 months (interquartile range, (IQR) 5-27). Survival times in months (vs the systematic review) were: 90th percentile 8 (9); 75th percentile 16 (19); and median 34 (33). Follow-up duration was insufficient to estimate the 25th and 10th percentiles, similar to the systematic review. Liver metastases were associated with shorter survival (HR = 1.74, 95% CI, 1.1-2.76, P = .02). Seventy percent of patients had a baseline cardiac assessment. Five patients (3.9%) developed symptomatic cardiac toxicity, similar to clinical trials. CONCLUSION: Survival and cardiac toxicity rates for women starting trastuzumab in routine practice were comparable to clinical trials. Oncologists can use clinical trial data as a reference point when explaining survival outcomes to women with HER2-positive MBC.