Bristol-Myers Squibb Co on Thursday filed a lawsuit against Merck & Co Inc for allegedly infringing its immunotherapy patent. The company is seeking unspecified damages.

Immunotherapy is a mechanism that uses the body's own immune system to eliminate cancer cells.

In its lawsuit filed in the U.S. District Court of Delaware, Bristol-Myers said Merck was planning to exploit its invention with a later-developed treatment, pembrolizumab, violating the company's May 20 patent.

U.S. regulators on Thursday approved the use pembrolizumab, as a treatment for patients with advanced melanoma who are no longer responding to other therapies.

Bristol-Myers is using its patented technology to develop its own drug, nivolumab, which is being tested in different areas of cancer including melanoma.

The company also plans to file an application with the U.S. Food and Drug Administration by the end of this month for use of the drug, which is approved in Japan, for patients with advanced melanoma.

Other pharmaceutical companies including Roche Holding AG and Novartis AG are also in the process of developing similar drugs.

According to the American Cancer Society, about 76,100 new melanomas will be diagnosed this year. The disease is the most dangerous kind of skin cancer and can originate in any part of the body that contains pigment-containing cells.

Both Bristol-Myers and Merck could not be reached for a comment outside regular working hours.

The case is Bristol-Myers Squibb Co and Ono Pharmaceutical co ltd v. Merck & Co Inc, U.S. District Court, for the district of Delaware, Wilmington No. 14-CV-01131