May 31 (Reuters) - As a wider range of drugs that enlist the body's immune system to fight cancer become available, clues about which combinations will prove most effective are expected at the upcoming meeting of the American Society of Clinical Oncology.
The ASCO meeting, which starts Friday in Chicago, draws tens of thousands of specialists from around the world. This year it will feature more than 250 presentations involving immune-system-boosting drugs known as checkpoint inhibitors, with the lions share of research focused on drugs that target a protein called PD-1, including Merck & Co Inc's Keytruda, Bristol-Myers Squibb Co's Opdivo and Roche Holding AG's Tecentriq.
The drugs work by releasing molecular brakes, or checkpoints, that tumors use to avoid the bodys immune system. That allows the immune cells to recognize and attack cancer cells the same way they fight infections caused by bacteria or viruses. For certain cancers, like melanoma, the treatments can mean long-term survival for around 20 percent of patients. Researchers and drugmakers are now focused on testing whether these new drugs can become more powerful, and treat more people, in combination.
"We need to probably add to those regimens to have the best chance of eradicating all of the clones that lead to (drug) resistance," said Craig Tendler, head of late development and global medical affairs at Johnson & Johnsons Janssen division. "To get from 20-25 percent of patients up to 50 percent and beyond is going to require other approaches."
In some cases, researchers are combining different types of checkpoint inhibitors. They are also testing the new treatments with older drugs like chemotherapy.
"There are hundreds and hundreds of combination trials," said Brad Loncar, manager of the Loncar Cancer Immunotherapy ETF . "We are still waiting for a winner to emerge."
The global market for cancer immunotherapies alone is expected to grow more than fourfold to $75.8 billion by 2022, according to research firm GlobalData.
Other checkpoint inhibitor drugs that will be in focus at ASCO include those that target the CTLA4 protein, such as Bristol's Yervoy, and those that target IDO1. A small study released earlier this month showed that combining Merck's Keytruda with an experimental IDO1 drug from Incyte Corp led to a high rate of durable responses in patients with advanced lung cancer. Separately, U.S. regulators approved a combination of Keytruda and chemotherapy for previously untreated advanced lung cancer.
"As far as which combinations we think will look better ... it is a little early," said Dr. Bruce Johnson, chief clinical research officer at Boston's Dana-Farber Cancer Institute and ASCO's incoming president.
New data is also expected on a different class of experimental drugs that recruit immune system cells, known as CAR-T therapies, from companies including Kite Pharma Inc , Juno Therapeutics Inc and Novartis AG .
The ASCO meeting will feature key trial results on the best use of J&J's Zytiga for men newly diagnosed with high-risk, metastatic prostate cancer and of AstraZeneca Plc's ovarian cancer drug Lynparza in breast cancer.
New data on treating genetically-defined cancers will be presented from a wide range of companies including Loxo Oncology Inc and Roche, which aims to insure use of its newer targeted breast cancer drug Perjeta before its older, multibillion-dollar drug, Herceptin, loses patent protection. (Reporting By Deena Beasley; Editing by Andrew Hay)