European regulators have conditionally approved Pfizer's first-in-class lung cancer drug Xalkori.

Specifically, the European Commission has given permission for the drug's use in adults with previously treated ALK-positive advanced non-small-cell lung cancer (NSCLC).

As per the terms of the conditional approval, Pfizer must hand over data from its recent Phase III PROFILE 007 trial to the European Medicines Agency for review, which may then award the drug traditional clearance it if considers the data strong enough to do so.

Earlier this year, Pfizer said that top-line data from the study shows that Xalkori (crizotinib) significantly improved progression-free survival in previously-treated patients with ALK-positive advanced NSCLC.

The drug is a first-in-class, oral ALK inhibitor, which works by blocking signaling in various cell pathways believed to play a crucial role in the growth and survival of tumor cells.

According to Jean-Charles Soria, professor of Medicine and Medical Oncology at South-Paris University and cancer specialist at Institut Gustave Roussy, France, Xalkori represents a "major advancement" in the field of metastatic NSCLC, as it brings to eligible patients "an oral compound that can achieve tumor shrinkage and delay disease progression".

Xalkori was approved by the US Food and Drug Administration in August 2011, and analysts are predicting peak annual sales of more than $2 billion.