Early results of an early phase trial study of pembrolizumab (Keytruda, MK-3475)I women with triple-negative breast cancer (TNBC) are intriguing.
At first glance the data seems lackluster; the non-randomized study has so far yielded an overall response rate of 18.5%.
However, the findings drew attention at the San Antonio Breast Cancer Symposium, in part because TNBC is a notoriously hard-to-treat form of the disease.
Keytruda is a monoclonal antibody given by infusion. When it binds PD-1 it can unleash the body’s normal immune cells to fight a tumor. Recently the FDA approved Keytruda for use in advanced melanoma. Last week, at the annual meeting for the American Society of Hematology, investigators reported preliminary findings that the drug is well-tolerated and may be helpful in Hodgkin’s lymphoma.
The KEYNOTE-12 study recruits patients with several types of malignancies including advanced head and neck cancer, bladder cancer, gastric cancer and a cohort of women with advanced TNBC. The phase 1b trial is designed to measure the safety, side effects and possible anti-tumor activity of Keytruda. Among women with breast cancer who received the drug in this trial, the median age was 51.9 years old.
A limitation of the findings is that among 32 women with refractory breast cancer who received Keytruda, only 27 could be evaluated for a response at the time of analysis. As reported, five of the women had sustained, measurable responses by RECIST criteria lasting over 40 weeks in three cases. One woman had a complete response. In addition, 26% had stabilized disease.
Unfortunately, one woman passed while in this study. Her death was attributed to disseminated intravascular coagulation, a severe blood disorder with impaired clotting.
In some ways, the results are somewhat promising for a group of patients with an extremely poor prognosis. An 18-20% response rate for a single agent, among women with heavily-treated refractory TNBC, is potentially helpful.