Rumors that Celgene Corporation is in talks to acquire Juno Therapeutics has caused Juno’s stock to rocket more than 50 percent to $68.80 in premarket trading.

It’s a deal that would make quite a bit of sense. Celgene is an oncology company, but its best-selling drug, Revlimid, for blood cancer, is losing patent protection, and there were some failures in its pipeline last year, so it needs to diversify its portfolio. Juno is well on its way to breaking into the CAR-T immuno-oncology field, although its trajectory has had its hiccups.

In April 2017, Juno shuttered its lead CAR-T program, JCAR015, because of patient deaths. But two months later it bounced back with positive interim data from another CAR-T program, JCAR017, which has since gone on to be even more promising. It also has a strong pipeline.

Yesterday morning, Michael Yee, an analyst with Jefferies, wrote in a note, "We are not surprised nor shocked to see this and view the potential acquisition as an incremental positive since it would consolidate long-term revenues and technological expertise, although we also acknowledge new revenues and external business development are favorable given that Celgene needs new revenue and already have rights to the majority of Juno’s pipeline."

It was only a week ago that Celgene announced it was buying Impact Biomedicines for $1.1 billion upfront. That deal has the potential to hit $7 billion if certain milestones are met.

Juno and Celgene have been partnered since 2015 in a 10-year deal to develop cancer and autoimmune treatments. BloombergMarkets notes, "A takeover of Juno, if it comes at a hefty a premium as the stock-market activity in the wake of the Journalreport suggests, would rank among Celgene’s largest-ever deals. In 2015, Celgene acquired Receptos, Inc. for $7.2 billion, gaining an experimental treatment called ozanimod being tested in Crohn’s disease, ulcerative colitis and multiple sclerosis."

Although the deal doesn’t seem all that surprising, and makes quite a bit of sense, not all analysts think it’s a great idea. Max Nisen, writing at the Bloomberg Gadfly, notes, "But buying Juno would be a risky bet on a catch-up effort in a crowded field."

He goes on to point out Juno’s earlier issues with patient deaths and that it was leading the field in CAR-T development until then, only to be beat out by bothNovartis and Gilead/Kite. "It has recovered since then," Nisen writes, "producing promising efficacy and safety data for next-up treatment JCAR17 in lymphoma patients. Should current data hold up, it may prove superior to rival offerings form Gilead Pharmaceuticals Inc.—which bought fellow cell-therapy pioneer Kite Pharma Inc. last summer—and Novartis. But the product is unlikely to hit the market until 2019. Gilead’s Yescarta is available in the U.S. to the patients that JCAR17 is intended to treat. Novartis’s Kymriah will most likely become available this year.’

And, of course, there’s no guarantee that data on Juno’s CAR-T product will hold up to further testing. That’s the very nature of clinical trials. Assuming the data is still good and the therapy is approved, Gilead and Novartis have plenty of time to dig into a strong market position.

Another question that remains is how much Celgene would be willing to pay. As of yesterday, Juno’s market cap was $5.2 billion. The company’s value has been on an upward trend since at least August, but it’s been rumored to be a choice acquisition target for some time, at least until it abandoned JCAR015, which took some of the shine off the stock. But over the last year, company shares have grown 139 percent.