Merck & Co.'s PD-1 inhibitor Keytruda shows promise in advanced triple-negative breast cancer

Merck & Co. on Wednesday said that its PD-1 inhibitor Keytruda (pembrolizumab) demonstrated an overall response rate of 18.5 percent in an early-stage study of patients with PD-L1 positive, advanced triple-negative breast cancer. The data from the Phase Ib KEYNOTE-012 trial were presented at the San Antonio Breast Cancer Symposium (SABCS).

In the study, 32 patients with triple-negative breast cancer determined to be positive for PD-L1 expression were treated with Keytruda at 10 mg/kg every two weeks, with 27 patients being evaluable for efficacy. Merck noted that most enrolled patients had previously received at least two prior chemotherapeutic regimens for metastatic disease, while 87.5 percent had received prior neo-adjuvant or adjuvant therapy.

The drugmaker said that the responses included one complete response and four partial responses, while stable disease was noted in another seven patients. Merck added that at the time of analysis, the median duration of response had not been reached with three of five responders on therapy for 11 months or more. The median duration to response was 18 weeks, and some measure of tumour shrinkage was observed in 33 percent of the study participants. Meanwhile, the progression-free survival rate at six months was 23.3 percent.

Merck stated that the safety profile of Keytruda was consistent with previous findings, with the most common adverse events including arthralgia, fatigue, myalgia and nausea. Principal investigator of the study Rita Nanda, who noted that there is currently no approved therapy for triple-negative breast cancer that has spread to other parts of the body, remarked that the findings suggested an "efficacy signal" that is worth investigating in further studies.

Alise Reicin, vice president of global clinical development, oncology at Merck Research Laboratories, said the results come from "patients with one of the most aggressive forms of breast cancer," adding "our Phase II study planned for the first half of 2015 will be an important next step for our breast cancer clinical programme." Also on Wednesday, Merck, the International Breast Cancer Study Group (IBCSG) and Breast International Group (BIG) announced the start of the PANACEA study, which will investigate whether the addition of Keytruda can reverse resistance to Roche's Herceptin (trastuzumab) in patients with HER2-positive breast cancer whose disease has spread while on Herceptin.

Keytruda was approved by the FDA in September for the treatment of advanced or resectable melanoma, marking the first clearance of a PD-1 inhibitor for any indication in the US. Merck also recently reported early-stage data suggesting the potential efficacy of Keytruda in transplant-ineligible and failure patients with relapsed/refractory classical Hodgkin lymphoma whose disease progressed on or after treatment with Seattle Genetics' Adcetris (brentuximab vedotin).

For related analysis on the PD-1 inhibitor class, read ViewPoints: Excitement but uncertainty shapes melanoma market as PD-1 inhibitors encroach and ViewPoints: Immuno-oncology movement into haematological cancers gathers pace.

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