(Adds more information on Bristol-Myers Phase III plan in final paragraph)
By Bill Berkrot
May 14 (Reuters) - When the world's leading cancer doctors meet in Chicago next month, new treatments from Merck & Co, Bristol-Myers Squibb Co and Roche Holding AG that help the immune system fight disease are expected to capture much of the spotlight.
The drugs, known as anti-PD-1 or anti-PDL1 therapies, are biotech medicines that work by blocking a tumor's ability to camouflage itself, thereby allowing T cells in the immune system to recognize and attack the cancer.
They have shown great promise against advanced melanoma - the deadliest of skin cancers - as well as advanced lung and kidney cancers, with relatively mild side effects, generating excitement among researchers and investors.
At the American Society of Clinical Oncology meeting in Chicago beginning May 30, researchers will for the first time present data on Roche's anti-PDL1 drug in advanced bladder cancer for which there have been few advances in decades.
Merck will have no less than 16 studies involving its highly touted anti PD-1 drug, MK-3475, including a first look at the drug as an initial lung cancer treatment. Early data released on Wednesday showed 36 percent of 45 patients had an initial immune response to the treatment. Merck will also provide results from the first trial of the drug in head and neck cancer.
Brief summaries, or abstracts, of thousands of studies to be presented at the ASCO meeting were released on Wednesday.
"This area should represent a major advance in cancer therapy and patient survivability," said Len Yaffe, portfolio manager for the healthcare fund StockDoc Partners. "Wall Street is increasingly recognizing the multibillion-dollar potential for cancer immunotherapies."
The potential for lasting effects of these drugs will be on display in a pair of studies involving the Bristol-Myers anti PD-1 drug nivolumab.
Researchers will present follow-up data from a 107-patient nivolumab study in metastatic melanoma showing that 41 percent were still alive after three years, an apparent leveling off from the 48 percent survival rate after two years.
Three-year survival with advanced melanoma was virtually unheard of prior to the advent of cancer immunotherapy.
In a trial of patients whose advanced kidney cancer had progressed following prior treatments, the mean overall survival was 25.5 months for the 2 milligram nivolumab dose.
Past kidney cancer studies of drugs currently in use have demonstrated a mean survival of about 14 months, said Fouad Namouni, Bristol's head of global development for nivolumab.
As drugmakers face greater scrutiny over how they price new therapies - with immuno-oncology expected to be among the most expensive - several studies will aim to identify which patients are most likely to benefit from the new treatments.
Researchers can now perform a test to determine the degree to which the PD-L1 protein is expressed on the surface of cancer cells. On a 0 to 3 scale, a score of 0 or 1 is considered PD-L1 negative, while 2 or 3 is deemed PD-L1 positive.
If early data is confirmed in larger trials, this class of immunotherapies could become standalone treatments for some patients, while PD-L1 negative patients may require combination or alternative therapies, according to some researchers.
In a small, Phase I study of Bristol's nivolumab in previously untreated patients with advanced lung cancer, five out of 10 PD-L1 positive patients saw their tumors shrink by at least 30 percent. No such responses were seen among 7 PD-L1 negative patients. Roche also saw half of the 20 PD-L1 positive patients in its bladder cancer trial respond to its drug.
Namouni said Bristol would focus on PD-L1 positive patients only in a large Phase III lung cancer trial of previously untreated subjects. Its Phase III studies of those who had received prior treatments will include PD-L1 negative patients. (Reporting by Bill Berkrot; Editing by Michele Gershberg and Andre Grenon)