SAN FRANCISCO (TheStreet) -- The new class of cancer immunotherapy drugs led by Merck's (MRK) Keytruda and Bristol-Myers Squibb's (BMY) Opdivo have already generated tremendous excitement for their ability to shrink solid tumors. Now, the drugs are also demonstrating equal promise in blood-related cancers.
Patients with very advanced Hodgkin lymphoma unresponsive to any currently approved medicines were able to achieve complete remissions of their disease following treatment with Merck's Keytruda and Bristol's Opdivo, according to results from separate, early-stage studies being presented for the first time at the American Society of Hematology (ASH) annual meeting here.
These studies demonstrate that so-called checkpoint inhibitors can prime a patient's own immune system to identify and kill certain types of blood cancer cells just like they do with solid tumors such as melanoma and lung cancer.
Based on the early data from these studies, Merck and Bristol-Myers are moving ahead with larger studies necessary to get their respective drugs approved as new treatments for blood-related cancers.
The Merck study enrolled 29 patients with relapsed/refractory Hodgkin lymphoma, meaning their cancer had returned and was growing despite treatment with Seattle Genetics' (SGEN) Adcetris, the only drug currently approved for such advanced disease. Twenty patients enrolled in the study failed a prior stem cell transplant, while the remaining nine patients were either ineligible or refused a stem cell transplant.
Six of the 29 patients (21%) treated with Merck's Keytruda achieved a complete remission, meaning there was no evidence of disease in their bodies. Another 13 patients achieved partial remission, for an overall response rate to Keytruda of 66%.
At the time of the analysis, 17 of the 19 patients with either a complete or partial remission were still responding to Keytruda. The median duration of response has not yet been reached in the study.
In all, 27 of the 29 Hodgkin lymphoma patients treated with Keytruda showed some level of response or tumor shrinkage in the study.
"We're very excited about these results because the study enrolled highly refractory patients who had failed all current therapies including [Adcetris] and transplant," said Dr. Alise Reicin, a Merck vice president in charge of oncology drug development.
Bristol-Myers conducted a similar study of its checkpoint inhibitor Opdivo in 23 patients with relapsed or resistant Hodgkin lymphoma, 87% of whom had failed more than three previous therapies, including stem cell transplant and Seattle Genetics' Adcetris.
Four of the 23 patients (17%) achieved a complete remission following treatment with Opdivo. The overall response rate in the study (complete and partial remissions) was 87% after an average follow up of 40 weeks.
Survival data was not reported from either the Merck or Bristol-Myers studies. Adverse events reported across both studies were similar to what's been seen from Keytruda and Opdivo studies in solid tumors.
Merck plans to start a larger phase II study of Keytruda in Hodgkin patients in the first half of 2015. Bristol-Myers has a phase II study of Opdivo in Hodgkin patients already underway. Both studies, if positive, are likely to be sufficient for regulatory approval because the patients enrolled have no approved treatment options remaining.
Both companies are also likely to explore use of their respective drugs in earlier lines of Hodgkin therapy, based on the strong efficacy seen in the most sick patients. This development could become a significant competitive threat to Seattle Genetics' Adcetris. There's also the possibility that checkpoint inhibitors and Adcetris could be complementary. Combination therapies are being considered for studies.
Outside of Hodgkin lymphoma, Merck is also studying Keytruda in other blood cancers, including multiple myeloma, myelodysplastic syndrome and non-Hodgkin lymphoma.
Merck secured U.S. approval for Keytruda in advanced melanoma in September. Bristol-Myers' Opdivo is approved for melanoma in Japan and is under review for the same indication in the U.S.
The class of immunotherapies known as checkpoint inhibitors work by blocking a protein known as PD-1 which cancer cells use to hide from a patient's immune system. Blocking PD-1 makes tumors visible to killer T cells.