After Imfinzi's key non-small cell lung cancer trial failure last year, AstraZeneca has some good news to report in lung cancer. But it's from the much smaller field of small cell lung cancer where Roche’s Tecentriq is a step ahead.

In patients with newly diagnosed extensive-stage small cell lung cancer, a combination of Imfinzi and standard chemo beat chemo alone at extending lives in a phase 3 trial, AstraZeneca saidThursday.

Detailed data have not been shared, but AZ said the survival benefit in the Caspian trial was statistically significant and clinically meaningful.

If ultimately approved, Imfinzi will have a chance to compete with Roche’s rival PD-L1 inhibitor Tecentriq, which in March became the first immuno-oncology agent to get an FDA nod in first-line SCLC.

Of course, industry watchers will be keeping a close eye on the exact overall survival numbers. In Roche’s separate phase 3 IMpower133 study, the Tecentriq-chemo combo extended patients’ lives by two more months on top of solo chemo’s 10.3 months.

But AZ was quick to point out its Caspian trial offers "the flexibility of combining immunotherapy with different platinum-based regimens in small cell lung cancer, expanding treatment options," Jose? Baselga, AZ’s recently installed oncology R&D chief, said in a statement.

The Caspian trial tested Imfinzi in tandem with chemo drug etoposide and either one of two platinum-based chemo, carboplatin or cisplatin. In comparison, the Roche regimen was only for carboplatin.

Caspian will continue, as investigators are still waiting for final survival analysis from adding AZ’s very own CTLA4 candidate tremelimumab to the regimen, the company said. Imfinzi alone and the Imfinzi-tremelimumab dual checkpoint inhibitors were the protagonists in last year's closely-watched Mystic trial flop in previously untreated non-small cell lung cancer.

NSCLC is a much larger indication than SCLC. About 10% to 15% of lung cancer cases are SCLC, and of them, two-thirds are in an extensive stage when diagnosed.

Imfinzi is already approved in unresectable, stage III NSCLC, where it's enjoyed competition-free sales. In the first quarter, it ginned up $295 million, slightly above the Street’s expectations. By AZ’s estimate, the growth rate is putting the drug on track to cross the blockbuster threshold this year. But it’s still behind Tecentriq’s 336 million Swiss francs ($344 million) in the same period.

Meanwhile, Merck & Co.’s PD-1 inhibitor Keytruda, which recently racked up an FDA green light in third-line SCLC, is also being tested in the first-line setting. And the trial, dubbed Keynote-604, also offers the liberty to choose a platinum chemo. However, Bristol-Myers Squibb’s Opdivo, which was the first to get into SCLC with a third-line nod, has suffered setbacks as it tried to push into prior lines of treatment.

AstraZeneca is looking at a busy year ahead for Imfinzi. Besides SCLC, it’s also expecting results in first-line head and neck cancer—where Keytruda just secured two FDA approvals—and first-line bladder cancer. Two phase 3 trials, Poseidon and Neptune, in first-line NSCLC, will also read out this year.