Erasca shares fell after Revolution Medicines alleged that the company's development of its ERAS-0015 cancer treatment infringes on existing patents and relies on stolen trade secrets.

Shares of the clinical-stage oncology company slid 30% in post-market trading to $13.59 on Monday, after ending the market session down 11% at $19.15. The stock's price has soared more than five fold so far this year.

Erasca received a legal letter on April 24 from Revolution, a rival oncology company, alleging that ERAS-0015 is "substantially equivalent" to one of its patented treatments, according to a Securities and Exchange Commission filing on Monday.

In its letter, Revolution also alleged that a third party had misappropriated its trade secrets for a patent involving ERAS-0015 and that Erasca is liable under trade secret laws as a licensee, according to the filing. It also alleges that Erasca has improperly compared preclinical data of ERAS-0015 to Revolution's RMC-6236.

Revolution demanded that Erasca cease producing and selling ERAS-0015 in the U.S., according to the filing.

"The company believes the assertions in the letter are without merit and intends to contest the allegations vigorously," Erasca said in the filing.

On Monday, Erasca said its treatment ERAS-0015 showed positive preliminary Phase 1 results in patients with lung and pancreatic cancer. ERAS-0015 is a molecular glue designed to inhibit RAS-signaling in patients with RAS-mutant solid tumors. The preliminary data comes from the company's Phase 1 trials being conducted in the U.S. and an ongoing Phase 1 trial in China.