In addition to assessing the impact of Merck’s $8.9 billion-Cubist acquisition, which was soon eclipsed by news that Cubist lost patent protection for one of its key antibiotics, investors are also navigating clinical trial results about Merck’s headline immuno-oncology therapy Keytruda (pembrolizumab).

The FDA approved Merck’s Keytruda in September for advanced or unresectable melanoma who are no longer responding to other drugs. The company is exploring the drug’s uses across 30 tumor types.

Merck announced at the San Antonio Breast Cancer Symposium Wednesday that 18.5% of patients in a Phase-1b clinical trial among  PD-L1 positive, advanced triple-negative breast cancer had a response. Leerink analyst Seamus Fernandez noted in a morning assessment that the news was disappointing, even though it is better than the typical 10% response rate among this hard-to-treat patient group.

Triple-negative breast cancer refers to cancer that responds neither to hormone treatments and HER2-targeted therapies. The non-profit estimates that between 10% and 20% of breast cancers are triple-negative, and notes, as did Merck in its statement, that this cancer is among the more aggressive breast cancers. adds that the five-year survival rate for patients with this form of the disease tends to be lower than for patients with other forms.

PD-1 inhibitors have been a major focus of pharmaceutical companies, and Evercore ISI analyst Mark Schoenenbaum wrote in an October research note why, saying they may end up as “’cornerstone therapy for many tumors.”

Merck said in a statement that it expects to move this Phase-Ib Keynote trial into Phase II during the first half of next year. The company followed the triple-negative clinical trial results with a separate announcement that it was also testing Keytruda with trastuzumab (Genentech’s Herceptin) among HER2-positive breast cancer patients to see if its PD-1 inhibitor can overcome Herceptin resistance when the two are used together.

The company rolled out additional clinical trial information Monday, noting that early-stage trials indicated effectiveness among Hodgkin’s lymphoma patients. Partner Amgen announced Monday that the two companies are also seeing how Merck’s Keytruda and Amgen’s talimogene laherparepvec work with regionally or distantly metastatic melanoma. Amgen said in a statement Monday that it has already started enrolling patients in the clinical trial, which is known as Panacea.