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Seattle Genetics CEO Clay Siegall. (Seattle Genetics Photo)

Seattle Genetics, a biotechnology company that develops antibody-based cancer treatments, announced Wednesday that it will acquire Cascadian Therapeutics and the company’s small-molecule breast cancer treatment for about $614 million, or $10 per share.

To help fund the move, Seattle Genetics is also preparing for a $550 million stock offering. The company declined to comment on plans for Cascadian’s staff and leadership.

Cascadian’s stock had jumped over 70 percent to $10.16 by 8:30 a.m. PT, while Seattle Genetics’ dropped about 4 percent to $53.58.

Cascadian is developing a small molecule drug called tucatinib. The drug can attack cancers that express HER2, a receptor that is very common in solid tumor cancers including breast, colorectal, ovarian and gastric. The drug is in the final stage of FDA approval, which is needed before it can go to market.

“This acquisition would enhance our late-stage clinical pipeline with a potentially best-in-class, orally available and highly selective TKI for patients with HER2-positive metastatic breast cancer,” Seattle Genetics CEO Clay Siegall said in a news release. “Beyond breast cancer, we believe there may be opportunities for tucatinib in other tumor types, such as HER2-positive metastatic colorectal cancer. Cascadian’s pipeline also includes a preclinical immuno-oncology agent. We look forward to welcoming the team at Cascadian Therapeutics and continuing the momentum of the tucatinib development program.”

Seattle Genetics’s own treatments use antibodies, part of the immune system, to send cancer-killing drugs directly to cancer cells. The technology is called an antibody-drug conjugate.

The company already has one treatment on the market — Adcetris, which treats several kinds of blood cancers and has been a success on the market. It also has treatments for solid tumor cancers in the pipeline, including a treatment that is being studied in HER2-negative breast cancer and triple negative breast cancer.

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