US drugmaker AbbVie has reached final agreement to acquire compatriot Pharmacyclics and the company's flagship asset Imbruvica (ibrutinib), which it describes as "a highly effective treatment for hematologic malignancies."

AbbVie said the agreement will enhance its clinical and commercial presence in oncology, strengthen its already robust pipeline and establish its strong leadership position in hematological oncology - "an attractive and rapidly growing market, now approaching $24 billion globally."

The deal, which the Chicago-based firm said also has the potential to leverage AbbVie's immunology expertise for the development of Pharmacyclics' immunology program, values the takeover candidate at around $21 billion.

Imbruvica is a Bruton's tyrosine kinase (BTK) inhibitor approved for use in four indications to treat three different types of blood cancers including chronic lymphocytic leukemia, mantle cell lymphoma and Waldenstrom's macroglobulinemia. It received initial US
Food and Drug Administration (FDA) approval in 2013 and is currently approved in more than 40 countries.

According to Abbevie, Imbruvica is the only therapy to have received three Breakthrough Therapy designations by the FDA. "Significant opportunity exists with further Imbruvica indications, including solid tumors," it added