Onyx Pharmaceuticals Inc. (ONXX) agreed to acquire privately held Proteolix Inc. for up to $810 million, giving Onyx a foothold in the $16 billion hematological malignancies market.

Biopharmaceutical company Proteolix's drug candidate carfilzomib, which targets hematological malignancies and tumors, is in multiple clinical trials - including an advanced midstage trial for patients with relapses and refractory multiple myeloma.

Under the deal, Onxy will pay $275 million in cash when the transaction closes, which expected in the current quarter. It also agreed to pay an additional $40 million next year if the drug reaches a development milestone and up to $535 million if it receives regulatory approvals in the U.S. and Europe. Of the $535 million, about $170 million requires the drug candidate to receive accelerated approval.

Like many drug development companies, Onyx has struggled to be profitable.

Onyx plans to present new data on carfilzomib at the American Society of Hematology meeting in December and release data from the midstage trials during the second half of next year.

The deal comes after Onyx's cancer therapy Nexavar missed its main goal in a Phase II trial in breast cancer last month. Onyx and partner Bayer AG (BAYRY, BAYN.XE) reported a "positive trend" towards improvement in progression-free survival and patients will be followed to determine any overall survival benefit.

Shares closed at $26.90 on Friday and didn't trade premarket. The stock is down 20% this year.

-By Tess Stynes, Dow Jones Newswires; 201-938-2473; Tess.Stynes@dowjones.com;