Pharmaceutical firm Gilead Sciences has just put up a cool $11.9 billion to acquire Kite Pharma, which has developed a genetic engineering approach for treating cancers.

The investment is a clear sign that gene therapy applied to cancer is a powerful—and commercially attractive—new technology. Kite, which is one of our 50 smartest companies of 2017, has developed a pioneering treatment for use against blood cancers such as lymphoma. It takes some of an individual's immune cells, known at T cells, then reprograms their DNA so that they can attack the disease. The resulting CAR-T therapy, as it’s known, is one of several being developed by the likes of Novartis and Juno Therapeutics to treat cancer, and they all appear to show huge promise for curing the disease.

The move is a clear sign that there’s huge commercial interest in the new form of cancer therapy. But the staggering valuation of Kite also hints at a potential problem for patients wishing to make use of the treatment in the future: cost. Just last week, Kaiser Health News ran a report on the potential pricing of the Novartis version of the therapy, and sources told it that it would "cost a fortune," proving to be "a quantum leap more expensive than other cancer drugs." No official pricing for such therapies has yet been published, but a figure of $649,000 for a one-off treatment has been deemed justifiable for young patients with leukemia by the U.K.’s National Institute for Health and Care Excellence.

That may change over time, though, especially if the the same technique is successfully used to develop treatments for other forms of cancer. The latter is certainly what Gilead is hoping will happen. “We see it as a nice, sustainable oncology platform for decades to come,” says Gilead CEO, John Milligan, to the Wall Street Journal.