The financial terms of the agreement weren't disclosed.

The Phase 1 study will evaluate the safety and tolerability of the combination in patients with ALK-positive advanced or metastatic non-small cell lung cancer (NSCLC).

"This collaboration is just one example of the willingness of sponsors to work together in an effort to accelerate progress against some of the most difficult-to-treat cancers," said Dr Mace Rothenberg, senior vice president, clinical development & medical affairs, and chief medical officer, Pfizer Oncology.

This multi-center, open-label clinical study is expected to begin in 2015 and will be conducted by Pfizer.

"Understanding the effects of combining one drug, XALKORI, which inhibits an abnormally activated enzyme in patients with ALK-positive metastatic lung cancer, with the investigational drug, Pembrolizumab, which harnesses the body's immune system to fight cancer, is vital if we are to continue to advance the care of lung cancer patients," Dr Rothenberg emphasized.

"We are pleased to build upon our ongoing collaboration with Pfizer to evaluate potential combination regimens incorporating Merck's investigational immunotherapy Pembrolizumab," said Dr Eric Rubin, vice president, oncology, Merck Research Laboratories.

He continued, "Evidence from early studies of Pembrolizumab monotherapy together with XALKORI's proven targeted therapeutic approach provides the scientific rationale for evaluating this combination for the treatment of lung cancer."

Both companies previously announced plans to evaluate the safety and efficacy of Pembrolizumab in combination with Pfizer's small molecule kinase inhibitor axitinib (INLYTA) in patients with renal cell carcinoma.

Separately, Pembrolizumab plus Pfizer's PF-05082566 (PF-2566), an investigational immuno-oncology agent that targets the human 4-1BB receptor, will be evaluated in multiple cancer types.

These studies are expected to begin enrollment later this year.