For more than 20 years, trastuzumab has been prescribed for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The HER2 overexpression ratio in patients with breast cancer is approximately 20%. Izzet Dogan of Istanbul University Institute of Oncology, Istanbul, Turkey, and colleagues evaluated patients with HER2-positive breast cancer who received long-term trastuzumab treatment by examining prognosis, to derive predictors of complete response.
All patients included in the study were diagnosed with HER2-positive metastatic breast cancer and received long-term trastuzumab. For the retrospective analysis, for each of the patients, clinical, pathologic, demographic, and treatment data were obtained.
Response Evaluation Criteria in Solid Tumors was used to evaluate response rates of trastuzumab-based treatment.
Moreover, the study focused on cessation of treatment for the analysis, and looked at prognosis of patients who had been treated with trastuzumab-based therapy.
Ranging from 32.3 to 330.3 months, but maintaining a median follow-up of 123.3 months, the study included 80 patients whose median age was 43 years. Patients received treatment with trastuzumab-based therapy for a median of 62 months (range, 12-191 months).
The percentage of de novo metastatic patients was 33.8%.
An analysis of all patients who had a pathologic HER2-overexpressed tumor that scored 3+ was 71.3% by immunohistochemistry or scored 2+ was 28.7% by immunohistochemistry confirmed with fluorescence in situ hybridization.
Overall survival statistics of 5, 10, and 15 years were found to be 96.1%, 86.8%, and 60.5%, respectively. In 75% of the patients, a complete response was detected. Median time to complete response was 14.4 months and ranged from 2.4 to 47.8 months.
The following variables were not statistically significant predictors for complete response: age at diagnosis, bisphosphonate treatment, de novo metastatic disease, menopausal status, and palliative radiotherapy.
Yet, the use of endocrine therapy (P = .019) with trastuzumab and the number of metastatic sites (P = .016) were statistically significant. Twelve patients ceased treatment with the trastuzumab regimen during the study period, 33% patients continued receiving aromatase inhibitor therapy, and 66.7% of patients received no treatment.
After cessation of trastuzumab therapy, recurrence was not detected in patients at a median follow-up of 44.7 months (range, 11.6-66.6 months).
The investigators concluded that in the HER2-positive metastatic breast cancer setting, trastuzumab-based therapy can support a full recovery. Discontinuation of therapy may be appropriately considered for patients who have achieved a long-term complete response. Aromatase inhibitor therapy should continue to be prescribed to hormone-positive patients. Predictors of complete response are the number of metastatic sites and the use of endocrine therapy with trastuzumab.
Source: Dogen I, Aydin E, Khanmammadov N, et al. Termination of trastuzumab-based treatment after complete response in HER2-positive metastatic breast cancer. Presented at: 2020 San Antonio Breast Cancer Symposium, December 8-11, 2020. Abstract PS10-44.