LOS ANGELES (Reuters) – New compounds designed to harness the body's own immune system against tumours will be a focus of the biggest annual cancer meeting this week, where drugmakers will issue clinical data on hundreds of treatments.

The American Society of Clinical Oncology (ASCO) annual meeting starts on Friday in Chicago.

One of the studies topping the list for doctors and investors will be Bristol-Myers Squibb Co.'s melanoma and lung cancer data for ipilimumab, a leading experimental drug. If approved by regulators, it could have sales of $425 million by 2014, according to Thomson Pharma.

Ipilimumab is part of the "immunotherapy" class of drugs, which includes antibodies that target immune system cells. The category also includes therapeutic vaccines designed to stimulate the immune system to attack malignant cells. "You will hear about successful manipulation of the body's immune system for treatment of advanced cancers," ASCO president Dr. Douglas Blayney, of the University of Michigan Medical School, said in a telephone interview.

Ipilimumab is a bioengineered antibody that boosts the body's immune response by interfering with a protein called CTLA-4, which acts as a brake on immune system cells.

By temporarily removing this brake, the hope is to unleash the immune system to find and destroy the cancer.

Cancer drugs have become popular with drugmakers, as they are less vulnerable to competition than other franchises and tend to command higher prices. The World Health Organisation has forecast that the global incidence of new cancer cases will increase to more than 20 million in 2025 from 12 million in 2008. Bioengineered antibodies have become some of the world's most widely used cancer therapies, including Avastin, sold by Switzerland's Roche Holding AG for treating various types of colon, breast, lung and other cancers.

ASCO will feature positive trial data on Avastin, or bevacizumab, as a treatment for ovarian cancer as well as results from two failed trials of the drug in patients with prostate and gastric cancers. Avastin is designed to interfere with the blood supply to tumours and some clinicians have theorised that different cancer types may have different paths for blood vessel growth.

US regulators last month approved the first vaccine for cancer, Dendreon Corp's prostate cancer therapy Provenge, which will have a price-tag of $93,000.

Unlike traditional vaccines that prevent disease, Provenge is manufactured by taking cells from a patient's tumor and incorporating them into a vaccine, which is injected back into the patient with the aim of recruiting the immune system to fight the cancer.