The US Food and Drug Administration (FDA) has granted orphan drug designation to ImmunoGen’s investigational skin cancer drug IMGN901.

In an early-stage trial, the drug is being developed to treat Merkel cell carcinoma (MCC), which is a rare and an aggressive neuroendocrine skin cancer typically occurring on the head or neck.

IMGN901 uses a CD56-binding antibody with a potent cancer-cell killing agent DM1 attached to it and has shown promising results among the small number of MCC patients treated to date.

Orphan drug designation is granted by the FDA to drugs or biologics that treat a condition affecting fewer than 200,000 Americans and allows the drugmaker a marketing exclusivity of seven years in the US on approval.

The drug has also received orphan medicinal product designation from the EU Committee for Orphan Medicinal Products for MCC treatment.

The company now plans to initiate the drug’s pivotal testing for MCC in 2011.