By Deena Beasley
(Reuters) - A highly anticipated new immunotherapy from Merck & Co Inc proved effective in patients with advanced melanoma as well as some with lung cancer or head and neck cancer, according to early-stage studies presented on Monday.
Merck filed in January for U.S. Food and Drug approval of MK3475, now known as pembrolizumab, as a treatment for melanoma, the deadliest form of skin cancer. But the drug's biggest sales opportunity is expected to be in treating lung cancer, which causes the most cancer deaths in the United States each year.
The drug is part of an emerging class of medications that work by blocking a protein called PD-1, or Programmed Death receptor, used by cancer cells to evade the body's immune system.
Morningstar has estimated that Merck's peak annual sales of pembrolizumab could reach $6 billion.
A Phase I study in 411 patients with melanoma that had spread to other parts of the body found that 69 percent were alive after a year of treatment. At 18 months, researchers estimated that overall survival was 62 percent, with some patients on the drug for more than two years. The findings were presented at the American Society of Clinical Oncology meeting in Chicago.
Patients with metastatic melanoma often have high levels of PD-L1 protein in their tumors. When PD-L1 attaches to its receptor PD-1 on immune cells, tumors are able to hide from the immune system; drugs that target either PD-L1 or PD-1 inhibit this interaction.
More than half the patients in the melanoma trial had previously been treated with ipilimumab, which is sold by Bristol-Myers Squibb Co under the brand name Yervoy. It is part of a class known as CTLA-4 blockers that work by unleashing a different part of the immune system.
Overall, 34 percent of patients had tumor shrinkage after treatment with Merck's drug, including 40 percent not treated with ipilimumab and 28 percent whose cancer worsened despite ipilimumab.
The most common immune-related adverse events included thyroid problems. Four percent of patients stopped treatment due to side effects.
"In general, this is probably the safest drug I have ever used in metastatic melanoma patients," said Dr Antoni Ribas, professor of hematology-oncology at the University of California, Los Angeles and the study's lead investigator.
A separate arm of the trial - 45 previously untreated patients with advanced non-small cell lung cancer who tested positive for PD-L1 - showed by one measurement that 47 percent had tumor shrinkage. A different measurement showed that 26 percent of those patients responded to the drug.
Two different methods were used because standard measures can underestimate the impact of drugs that work by targeting the immune system, said Dr Alise Reicin, Merck vice president oncology.
She estimated that around 70 percent of advanced non small-cell lung cancer patients have tumors that express PD-L1.
Merck said the median duration of response had not been reached in the lung cancer trial, with some patients continuing on the drug for at least a year.
Results for a trial segment involving 217 patients with advanced non-small cell lung cancer who had previously been treated with other drugs were slated for presentation at the ASCO meeting on Tuesday.
Dr Reicin declined to comment on when Merck would file for regulatory approval of pembrolizumab as a treatment for lung cancer. The company did say it plans to launch in September a Phase III study comparing the drug to chemotherapy in previously-untreated patients with PD-L1 positive, advanced NSCLC.
Merck on Sunday presented data from a small number of patients with advanced head and neck cancer who were treated with pembrolizumab. Of the patients deemed to be high expressers of PD-L1, 45 percent experienced tumor shrinkage, compared with 11 percent for the overall group.
The FDA is slated to decide by late October whether to approve pembrolizumab for patients with advanced melanoma previously treated with ipilimumab.
Merck is studying pembrolizumab across more than 30 types of cancers, as a stand-alone treatment and in combination with other drugs.
Drugs targeting either PD-1 or PD-L1 are also under development at companies including Roche AG, AstraZeneca Plc and Bristol-Myers.