NEW YORK, March 27 (Reuters) - Merck & Co ( MRK ) said

on Thursday that it plans to launch a subcutaneously injected

version of its blockbuster cancer immunotherapy Keytruda in the

U.S. on October 1, and expects to hit peak adoption rates of the

new version within two years.

The subcutaneous version of the drug is not yet approved by

the U.S. Food and Drug Administration, which has a target of

September 23 to decide. By injecting Keytruda under the skin

rather than intravenous delivery, it will reduce the time it

takes for patients to receive the medicine, the drugmaker said.

"We'll be shipping product immediately following approval,

in the first week or two following approval is the expectation,

and we'll have more than enough supply to meet the market

demand," Joanne Monahan, a senior vice president in Merck's ( MRK )

oncology division, said in an interview.

The company expects peak adoption of the drug to be at least

30% to 40% of patients on Keytruda, she added.

"We expect the greatest uptake, at least initially, in

patients who take monotherapy, oral combinations, and those who

have early-stage cancers," Monahan said.

Keytruda, which is approved to treat many types of cancer,

is the world's top-selling prescription medicine, with nearly

$30 billion in sales in 2024.

In data the company is presenting at the European Lung

Cancer Congress, it said the median injection time per

subcutaneous dose was two minutes, down from around 30 minutes

for a Keytruda infusion.

Merck ( MRK ) has relied on Keytruda to fuel its growth for years. It

hopes the intellectual property protection from the subcutaneous

version can help protect against copies of the drug as key

Keytruda patents begin to expire in 2028.

The company hopes to start selling the subcutaneous version

of Keytruda in Europe in early 2026, Monahan said.

South Korea-based drugmaker Alteogen is

developing and manufacturing an enzyme used with the

subcutaneous formulation of Keytruda.

While Merck ( MRK ) and Alteogen could face a potential patent challenge

from biotech Halozyme Therapeutics ( HALO ) over the enzyme,

Merck ( MRK ) said it will not delay the launch of the drug.

"We believe we have a very strong position relative to the

claims from Halozyme," Merck's ( MRK ) Monahan said.