The Food and Drug Administration has agreed to give Eli Lilly's (LLY 0.31%) cancer drug selpercatinib a priority review, which will shave four months off the review time. The agency is expected to deliver a decision about the marketing application in the third quarter of 2020, although it could come sooner considering that the drug has been given a "breakthrough therapy" designation.

Eli Lilly inherited selpercatinib, which used to go by the code name LOXO-292, through its $8 billion acquisition of Loxo Oncology last year. Much of the value of that company was tied to its already-approved cancer therapy Vitrakvi, but selpercatinib was touted as the pipeline drug to watch.

Selpercatinib inhibits a protein called RET, which is involved in cell signaling in the presence of growth factors. The gene becomes altered in some tumors, leading to uncontrolled cell growth.

Doctor talking to a patient in front of a window

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Eli Lilly has applied for approval of the treatment in three different types of tumors with altered RET: non-small-cell lung cancer, medullary thyroid cancer, and thyroid cancer. Its application is based on data from the Libretto-001 phase 1/2 clinical trial, where initial results showed response rates between 45% and 77% in the different types of tumors. More recent results focused on lung cancer patients showed 68% of them responding to the treatment.

In December, the pharmaceutical company started two phase 3 clinical trials: Libretto-431 in lung cancer patients and Libretto-531 medullary thyroid cancer patients. Both studies will enroll patients who hadn't been previously treated, so in addition to confirming the results from the phase 1/2 study, data from the new studies could be used to pursue an expanded approval that would increase the population of patients approved to be treated with selpercatinib.