German drugmaker Merck KGaA and Pfizer have received breakthrough therapy designation for avelumab as a second-line treatment for metastatic Merkel cell carcinoma.

Avelumab is an anti-PD-L1 IgG1 monoclonal antibody designed for use with difficult-to-treat cancers, such as MCC, a rare and aggressive skin cancer with no approved treatment other than surgery, chemotherapy or radiation therapy.

The designation is based on preliminary data from a global Phase 2 study that showed the candidate may demonstrate a substantial improvement over current therapies. Final results will be presented next year.

The alliance between the two companies for joint development of the drug is less than two months old, yet already has produced its third FDA milestone, including orphan drug designation in September and fast track designation in October. Pfizer paid $850 million upfront for Merck KGaA’s immunotherapy pipeline last November.

The two companies also plan to investigate avelumab in other tumor types, such as head and neck cancer, mesothelioma, melanoma, non-small cell lung cancer, ovarian cancer, renal cell carcinoma and bladder cancer.

Separately, Merck KGaA announced last week that it had completed its $17 billion acquisition of St. Louis, Mo.-based Sigma-Aldrich, a chemicals and biologics company. The move will boost Merck’s supply chain and support the delivery of more than 300,000 products, the company has said.