AbbVie and Johnson & Johnson got a scare this Halloween, and it came in the form of an FDA approval for AstraZeneca’s Imbruvica rival.

Tuesday, the FDA greenlighted BTK inhibitor Calquence as a treatment for adults with mantle cell lymphoma who've received at least one prior therapy. The accelerated approval follows a breakthrough designation that AstraZeneca received just this August on the basis of strong phase 2 data.

Now, Calquence will go head to head with AbbVie and J&J’s blood cancer blockbuster—and the way analysts see it, the partners have reason to worry. In trials, the AZ medication has appeared “more tolerable” than Imbruvica, displaying lower rates of serious side effects, such as atrial fibrillation and major hemorrhage, Leerink Partners analyst Seamus Fernandez wrote in an August note to clients.

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AZ certainly hopes so. The British drugmaker gained access to Calquence in 2015, thanks to a $4 billion-plus deal with developer Acerta. And to that payoff, AstraZeneca isn’t stopping with MCL. It’s currently gunning for a Calquence nod in chronic lymphocytic leukemia, a larger market opportunity, and it's hoping those tolerability advantages hold up for Calquence in an ongoing, phase 3 CLL trial pitting it directly against the AbbVie-J&J star.

Meanwhile, Tuesday’s FDA blessing provides a needed boost for AstraZeneca’s oncology sales ambitions. Over the summer, the drugmaker’s closely watched immuno-oncology combo trial in first-line lung cancer came up short, throwing sales forecasts for its PD-L1 checkpoint inhibitor Imfinzi in doubt. AZ also recently struck a pact with Merck forking over half the rights to PARP standout Lynparza—and half the drug's potential sales.

“In what appears to be an admission of defeat in the initial I-O race, this agreement gives away half of Lynparza profits in order for AstraZeneca to take advantage of Keytruda’s broad development,” Fernandez wrote to clients at the time.