- Merck & Co. said Wednesday its cancer drug Keytruda, when combined with chemotherapy, helped keep patients with a difficult-to-treat form of breast cancer called "triple negative" alive and their disease in check longer than chemo alone.
- The positive results were observed in women in whom a certain amount of tumor and immune cells express a protein that makes Keytruda particularly effective. Patients in the trial, called KEYNOTE-355, were not previously treated and their disease had to have spread to other parts of the body.
- This data follows positive results from a study of patients with triple negative breast cancer who received Keytruda in a pre-surgical setting. Roche's rival immunotherapy Tecentriq already has won approval in this disease as part of a chemo regimen.
Now that Merck has secured a dominant position for Keytruda (pembrolizumab) in lung cancer, it is turning its attention to the second-biggest cancer killer of women.
Triple negative breast cancer is particularly difficult to treat, as the tumors do not have the receptors that make hormone therapy or Herceptin (trastuzumab) work. As a result physicians still must use systemic chemotherapies, making the tumor type an attractive area of research with new drugs.
KEYNOTE-355 enrolled women with triple negative disease and treated them with either the Keytruda-chemo combination or just chemo alone. Survival analyses were conducted among all women and two subgroups — women in whom at least 1% of tumor and immune cells express a protein called PD-L1, and those with at least 10% expression.
Merck said significantly more patients treated with the Keytruda combo in the 10% group were alive without disease progression than those treated with chemo alone. The company did not release detailed data, and said the trial will continue unchanged to determine whether the Keytruda combination also helps patients receiving it live longer.
Merck did not release any data from the other subgroups, causing Cantor Fitzgerald analyst Louise Chen to conclude the Keytruda regimen didn't help those patients.
Use of PD-1 blocking drugs like Keytruda and Bristol-Myers Squibb's Opdivo (nivolumab) in low expressors of PD-L1 has been tricky. As a single agent in non-small cell lung cancer, Keytruda can only be used in patients in whom at least 1% of their tumor cells express PD-L1, although it can be used in all comers as part of a chemo-combo.
Opdivo, meanwhile, stumbled when it tried to secure an approval in the first-line lung cancer population with a chemo-combo trial in patients whose tumors expressed 5% or more PD-L1.
Roche's Tecentriq (atezolizumab) won Food and Drug Administration approval with chemotherapy in triple-negative breast cancer patients in whom at least 1% of the immune cells infiltrating tumors express PD-L1. This sets a high bar for Merck, making the presentation of full KEYNOTE-355 something physicians will watch closely to see if Keytruda has a chance of matching Tecentriq.