Keytruda (pembrolizumab) was effective in treating triple-negative breast cancer regardless of whether women had received previous treatment, according to data presented at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago.
The studies, “Phase 2 study of pembrolizumab (pembro) monotherapy for previously treated metastatic triple-negative breast cancer (mTNBC): KEYNOTE-086 cohort A,” and “Phase 2 study of pembrolizumab as first-line therapy for PD-L1–positive metastatic triple-negative breast cancer (mTNBC): Preliminary data from KEYNOTE-086 cohort B,” were presented by researchers from the NYU Langone’s Perlmutter Cancer Center.
The trial included two groups of patients with advanced breast cancer that had spread to other locations. The first group was composed of 170 patients who had received extensive earlier treatment.
Keytruda is a checkpoint-blocking drug, and patients in the first group were included regardless of whether the checkpoint molecule PD-L1 was present in the tumor. The second group had not received earlier treatment and had tumors expressing PD-L1.
Among pre-treated patients, Keytruda shrank tumors by more than 30 percent in eight (5 percent) of the women, and stabilized disease in 35 women (21 percent) of the group. All eight patients who saw their tumors shrink lived for at least another year. In comparison, the patients who did not experience tumor regression had lower survival rates.
In the group that received Keytruda as their first treatment, 12 of 52, or 23 percent, saw tumors shrink by more than 30 percent. The treatment also stabilized disease in another 17 percent.
The study is the first triple negative breast cancer immunotherapy trial to date, and also is the largest study of immunotherapy in this cancer form.
“Our results suggest that this treatment as a single agent is effective for mTNBC [metastatic triple negative breast cancer],” said Sylvia Adams, MD, in a press release. Adams is an associate professor of medical oncology at Perlmutter Cancer Center and principal investigator of the study.
“Interestingly, we found that activity of pembrolizumab was seen in both PD-L1-positive and -negative tumors. These data are very encouraging, especially for a disease that is extremely aggressive and has limited treatment options when it metastasizes,” Adams said.
Researchers pointed out that the second group — previously untreated — was included to prove the safety of Keytruda in this patient group. But researchers also assessed the efficacy of the treatment in untreated patients. Both study goals seem to have been met, researchers said.
“This research contributes to a larger body of knowledge that could help provide better outcomes to women with few treatment options,” said Adams. “The data also suggest that immunotherapy administered earlier in the disease course is more beneficial, as response rates are much greater in first, compared to second- or later lines of therapy.”
But also patients in the pretreated group tolerated the treatment well. Only 12 percent of patients in the first group, and 8 percent in the second group experienced severe adverse events. Fatigue and nausea were the most common side effects reported. Four percent of patients in the first group, and none in the second group, stopped the treatment because of side effects.
According to Adams, more research is needed to identify biomarkers, test combination therapies, and to perform larger trials. But the data are, nevertheless, reason for optimism.
“Although only a small subset of women responded to the drug, within that subset pembrolizumab worked extremely well and responses were durable,” said Adams. “By causing fewer side effects and promoting longer life expectancy, pembrolizumab could help change the outcome of mTNBC.”