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A combination of the Merck & Co immunotherapy Keytruda and a different type of drug that also helps the immune system fight cancer from Incyte Corp led to a high rate of durable responses in a small, ongoing study of patients with advanced lung cancer, according to data released on Wednesday.

Incyte shares rose more than 6 percent to $128 in post-market trading, after the data became public.

Fourteen of 40, or 35 percent, of patients with advanced non-small cell lung cancer (NSCLC) who received Keytruda and Incyte's epacadostat experienced tumor shrinkage of at least 30 percent.

That is nearly double the overall response rate of about 18-20 percent seen with Keytruda alone in other studies.

BMO Capital Markets analyst Ian Somaiya, in a research note prior to release of the data, said a response rate of about 24-29 percent with a good safety profile would be viewed favorably.

Patients in the trial had received prior treatments, such as chemotherapy.

Twelve of the 14 patients who saw significant tumor shrinkage continued to respond to the therapy, with the longest so far at more than 500 days, indicating potential for long-lasting responses.

Epacadostat belongs to a new class of experimental drugs called IDO1 inhibitors which block an enzyme that protects tumors from the immune system. Keytruda is one of five approved drugs known as PD-1 or PD-L1 inhibitors that block a different mechanism tumors use to evade detection.

The companies believe the two can work together without the added toxicity observed with other combinations because PD-1 drugs are systemic, while IDO1 works specifically at the tumor site.

Three percent of patients discontinued treatment due to side effects, such as elevated liver enzymes, with one patient dropping out with brain swelling.

The data was included in a brief summary of the study that will be presented and likely updated next month at the American Society of Clinical Oncology meeting in Chicago.

There will also be data on the combination in bladder, kidney and head and neck cancers in addition to NSCLC. The companies are planning much larger Phase 3 studies in all of those cancers.

"We have an ambitious program and we believe (IDO1 inhibition) can be a very important piece for the next few years in improving immunotherapy for cancer patients," Incyte Chief Executive Herve Hoppenot said.

Lung cancer is by far the biggest oncology market with all companies in the immunotherapy field jockeying for position in that space.