(Bloomberg) -- Mirati Therapeutics Inc.’s shares fell the most in six months as results of studies combining its experimental lung-cancer drug with Merck & Co.’s top-selling immunotherapy disappointed investors. 

The combination of Mirati’s adagrasib and Merck’s Keytruda produced “relatively modest” efficacy, SVB Securities analyst Andrew Berens wrote in a note to clients. Shares of Mirati slid as much as 20% Tuesday in New York, the most intraday since May 27. 

San Diego-based Mirati is developing the drug to treat tumors bearing mutations in a cell-growth-related gene called KRAS that has proven difficult to target. If cleared, it would compete with Lumakras, a similar therapy from Amgen Inc. Both drugmakers are testing their drugs along with powerful immunotherapies to see if the combinations improve results. 

While Amgen’s combination trial yielded liver toxicities in many patients, Mirati’s studies with Keytruda showed lower levels of such side effects. Mirati has already applied for approval of the drug on its own, with a decision expected by Dec. 14. 

Mirati has drawn takeover interest from would-be purchasers, and has been weighing strategic options including a sale for some time, Bloomberg reported last month. Mirati will need to show compelling data for adagrasib’s use as a first-line therapy for any takeover thesis to have merit, B. Riley analyst Kalpit Patel wrote in a note.   

The findings from the studies will be presented Wednesday at the European Society for Medical Oncology’s 2022 Immuno-Oncology Annual Congress.

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