Keytruda encroaches on Jemperli's endometrial cancer territory

Merck & Co's KEYNOTE-158 trial of Keytruda has underpinned another FDA approval, this time for the PD-1 inhibitor as a single-agent therapy as a therapy for endometrial cancer with certain genetic mutations.

Keytruda (pembrolizumab) has been cleared for patients with advanced endometrial cancer whose tumours have microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) mutations, and have progressed after earlier systemic therapy, and who are not eligible for curative surgery or radiotherapy.

The green light means that Keytruda is muscling in on territory held by GlaxoSmithKline's rival drug Jemperli (dostarlimab), which was approved for patients with recurrent or advanced endometrial cancer with dMMR last year.

Jemperli has so far failed to make much headway in the market however, with sales of just $7 million last year, and the arrival of Keytruda threatens to dent its growth prospects.

KEYNOTE-158 is a phase 2 'basket' study focused on a broad range of cancers that and has already led to prior approvals for Keytruda, currently leading the market among the PD-1/PD-L1 inhibitor class with sales of $17.2 billion last year.

Data from the study has supported indications for tumour mutational burden-high (TMB-H) solid tumours, PD-L1-positive cervical cancer, and metastatic small cell lung cancer (SCLC), although the latter use was withdrawn after follow-up data failed to confirm its initial benefit.

In MSI-H or dMMR endometrial cancer, Keytruda achieved an objective response rate (ORR) of 46%, including 12% complete responses and 33% partial responses, after a median of 16 months' follow-up.

Two thirds of those who responded to the therapy (68%) did so for 12 months or more, while 44% had a response for at least two years.

It's the fourth gynaecological cancer approval for Keytruda meanwhile, which is also used to treat endometrial carcinoma without MSI-H or dMMR in combination with Eisai's multikinase inhibitor Lenvima (lenvatinib), and as a monotherapy and combination therapy for PD-L1-positive cervical cancer.

Endometrial carcinoma is the most common type of cancer affecting the uterus, of which there are around 65,000 cases every year in the US. Around a third of all endometrial carcinomas are MSI‑H or dMMR.