USA-HEALTHCARE-CANCER-COSTS Thomson Reuters May 1 (Reuters) - The U.S. Food and Drug Administration on Monday granted accelerated approval to AstraZeneca Plc's immuno-oncology drug to treat a type of bladder cancer in patients whose disease progressed despite chemotherapy.

The drug, called Imfinzi, works by helping the body's immune cells kill cancer, offering an alternative to toxic chemotherapy.

While not without side effects, immuno-oncology is a kinder option that also promises longer-lasting efficacy, although it costs more. Imfinzi, chemically known as durvalumab, belongs to a new class of oncology drugs called PD-L1 inhibitors that block a mechanism tumors use to evade detection from the immune system.

The drug was approved on Monday for use in patients with locally advanced or metastatic urothelial carcinoma.

The drug won accelerated approval, which enables the use of therapies for serious conditions to fill an unmet medical need based on data the agency believes is likely to predict a clinical benefit. AstraZeneca is required to conduct trials to confirm actual benefit to patients.

The FDA also approved a complementary diagnostic from Roche Holding AG to assess whether the PD-L1 protein is expressed in urothelial carcinoma tissue.

Imfinzi, considered one of AstraZeneca's most important pipeline drug, is being tested on its own and also in combination with another immune system-boosting therapy called tremelimumab in various cancers, including lung cancer.

U.S. listed shares of the company were up marginally at $30.47 in afternoon trading.