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 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.
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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.
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