MSD has secured approval from the US Food and Drug Administration (FDA) for its subcutaneous (SC) formulation of best-selling cancer asset, Keytruda (pembrolizumab).

This makes pembrolizumab and berahyaluronidase alfa-pmph, marketed as Keytruda QLEX, the first ever SC programmed cell death protein 1 (PD-1) blocker to get the FDA go-ahead.

Though the drug will have to be given to patients by Dr Joseph Thaddeus Beck, oncologist and medical director of the Highlands’ Clinical Trials Office, noted that the administration process will be faster, while offering patients “more choices” regarding where they receive their therapy.

Following the FDA’s decision, patients with 38 different solid tumour indications will gain access to Keytruda QLEX, including those with non-small cell lung cancer (NSCLC), triple-negative breast cancer and melanoma.

However, MSD, known as Merck & Co in the US, is hoping to also expand the SC formulation’s uses to haematological indications, with the company running a Phase II trial (NCT06504394) exploring the drug’s potential in two types of relapsed or refractory B-cell lymphomas.

Following its commercialisation, which is set to occur in the US by late September 2025, the big pharma forecasts that 30% to 40% of patients will be prescribed the SC drug instead of its intravenous (IV) counterpart within two years.

Patent cliff still looms for MSD

Since its market debut, Keytruda has become a dominant force in the solid tumour market, receiving approval in a wide range of indications and becoming the best-selling drug of all time, raking in $29.5bn for MSD in 2024 alone.

However, the drug’s commercial success now lies in the balance amid a looming patent cliff, which will see MSD lose its exclusive US market rights to Keytruda in 2028. This could be a devastating blow for MSD’s profits, as Keytruda accounted for nearly half of the company’s total sales in 2024.

Though the FDA approval of SC Keytruda is a step in the right direction for both patient centricity and MSD’s prospects, Israel Stern, oncology healthcare consultant at GlobalData, noted that its market edge may be dulled by “combination agents such as chemotherapies, antibody-drug conjugates (ADCs) and immunotherapies, which require intravenous administration”.

Jack Cuthbertson, senior healthcare analyst at GlobalData, echoed this sentiment, stating that “a SC formulation is unlikely to be chosen in a combination setting as it would not increase convenience”.

GlobalData is the parent company of Clinical Trials Arena.

However, both analysts acknowledged the enhanced convenience of Keytruda QLEX for those receiving the drug as a monotherapy or in combination with oral drugs, with Cuthbertson noting that individuals could “receive their dose in minutes rather than having to sit for an hour or more in the clinic”.

Moving forward, Stern notes that SC Keytruda’s sales will eclipse $1bn by 2026 in NSCLC alone, but after multiple IV biosimilars make it to market, the sales for QLEX “will mirror the total sales coming from biosimilars”.

Cuthbertson added: “Though Merck will be able to maintain higher sales for longer with Keytruda QLEX, the company will likely still see a drop off after loss of IV Keytruda’s patent exclusivity.

“This will be seen as not all patients will switch to the SC format, and biosimilars will still gain some market share.”