The combination of Merck & Co's immunotherapy Keytruda and chemotherapy boosted response rates in patients with advanced hard-to-treat squamous cell lung cancer, the company said.

An early look at results of a 204-patient trial showed an overall response rate of 58.4% for newly-diagnosed patients given Keytruda plus carboplatin and paclitaxel or Celgene Corp's Abraxane. That compared to 35% for chemotherapy alone.

The interim results will be discussed in greater detail next month at the annual meeting of the American Society of Clinical Oncology (ASCO), where data from several Keytruda trials and other therapies that help the immune system fight cancer will be presented. Data on a rival Roche drug from a similar squamous cell lung cancer trial will be featured at the meeting.

The duration of response was more than six months in 65.8% of patients given the Keytruda regimen compared with 45.6% of those who received chemotherapy alone, Merck said. Serious side effects were seen in 64.4% of Keytruda patients and 74.5% of patients given just chemotherapy.

Keytruda is the only immunotherapy approved in the United States to treat lung cancer patients who have not received prior treatment. That approval is for non-squamous non-small cell lung cancer (NSCLC), the most common form of the disease.

Squamous cell, a type of NSCLC, accounts for about 30% of all lung cancers, according to the American Cancer Society. People diagnosed with squamous cell lung cancer typically have a poor prognosis since the disease is often first diagnosed after it has spread.