The group representing Los Angeles doctors has joined with two patients to sue Health Net Inc for denying claims based on the insurer's definition of "medical necessity."

"They are denying these treatments because they are expensive," said Rocky Delgadillo, chief executive at the Los Angeles County Medical Association, which represents more than 6,500 physicians.

The lawsuit, filed in Los Angeles Superior Court, accuses Health Net of unfair and unlawful business practices. The managed care plan operates mostly in the western United States and has 2.3 million members in California.

"Medical care is complex, and sometimes there are differing medical opinions as to what constitutes medically necessary care," Health Net said in a statement on Thursday. "In these instances, Health Net carefully follows the guidelines established by the state of California's two regulators, the Department of Managed Health Care and the Department of Insurance."

One plaintiff in the lawsuit, Robert Mendoza, said he was forced to raise $30,000 from funds set aside for income taxes and proceeds from his wife's life insurance policy to pay for surgery for a rare type of prostate cancer after Health Net denied his request for coverage.

Kalana Penner, the other plaintiff, said she suffered from debilitating back, neck and head pain for 10 years before being treated with "occipital nerve stimulation."

The treatment was successful, but Health Net turned down the 33-year-old mother's request for a permanent device. That decision was reversed last year after the California Department of Insurance ruled that it should be covered.

"It's been life changing," said she said at a press conference in Los Angeles. "I was crippled by this disorder."