Thousands of results from clinical trials of cancer drugs were unleashed Wednesday evening ahead of the year's biggest event in cancer research, ASCO, or the American Society of Clinical Oncology meeting.
Among them were early data on AstraZeneca's experimental lung cancer drug, known as AZN9291. The medicine is designed to help patients whose cancer has mutated out of the reach of other drugs, a population for whom no medicines are approved.
And it's a key part of AstraZeneca's defense that Pfizer's $106 billion bid undervalues its prospects; the British company said earlier this month that the drug could draw about $3 billion in peak annual sales, compared with analysts' estimates of $1 billion to $2 billion.
In the study results released Wednesday, AZN9291 shrank tumors in more than half, or 51 percent, of the 177 patients in the study. The drug has been designated a "breakthrough therapy" by the U.S. Food and Drug Administration, a status designed to speed the path of important medicines to market.
So, a win for AstraZeneca, right?
Not so fast. While the data were well-received by analysts, some pointed to a similar drug from a much smaller biotech that may be even stronger.
Clovis Oncology shares jumped Wednesday evening in after-hours trading, and were up nearly 10 percent in early morning trading Thursday, on the prospects of its drug, CO-1686. While analysts said the Clovis data didn't present anything beyond what was already known, they noted some safety concerns with AstraZeneca's drug that could vault Clovis's ahead. (Track Clovis shares here.)
"A fairly robust update for AZD9291 shows increasing response rates, but also increasing adverse event rates and the mention of 5 cases of 'ILD-like events' that are under investigation (interstitial lung disease)," Cory Kasimov, an analyst with JPMorgan, wrote in a research note late Wednesday. "Bottom line, we continue to think 9291's efficacy data is competitive with 1686's, but we think this update is beginning to solidify 1686's safety benefit."
Further data from Clovis are expected at the meeting, to be held May 30 to June 3 in Chicago.
AstraZeneca also will have data on other drugs in its cancer pipeline, considered a key part of Pfizer's interest in the acquisition, including one in the hot area of immuno-oncology called MEDI4736. The company projects peak sales of that medicine of about $6.5 billion.
Immuno-oncology drugs aim to harness the body's immune system to fight cancer. They will be a big focus at this year's meeting, as they were last year. But data reported Wednesday on a combination of drugs in that space from Bristol-Myers fell short of expectations.
BMO Capital Markets analyst Alex Arfaei downgraded Bristol-Myers today to "market perform," citing disappointing results from a study combining the company's approved drug Yervoy with an experimental one called nivolumab.
"We were wrong to extrapolate the strong efficacy seen with Bristol's Nivo+Yervoy combo in melanoma to lung and kidney cancer," Arfaei wrote in a research note. "The future of this combo is uncertain, in our view."
Arfaei noted a "modest" response rate in tumor shrinkage of 22 percent and a "poor" side effect profile of the combination, and lowered his peak sales forecast for Bristol's immuno-oncology drugs to $12.9 billion in 2023, from $15.3 billion.
While the majority of data from ASCO was released Wednesday night, there is much more to come at the meeting itself. Stay tuned.
And while big pharmas are leading the show at this year's meeting, it's the more volatile biotechs that are leading the stock moves off Wednesday's data drop. Clovis gained, while Incyte tumbled.
Incyte presented data on its approved drug, Jakafi, in a potential expanded use for pancreatic cancer. Analysts were watching closely to see what marker the company would choose to help identify patients for whom the drug would work best; it turned out to be C-reactive protein, or CRP, a marker of inflammation. The study showed positive trends toward helping patients with pancreatic cancer, though the results weren't statistically significant.
The company also presented data from a very early study of its immunotherapy drug INCB24360, which aims at a target called IDO, in melanoma. The study combined Incyte's drug with Bristol's Yervoy. Of just eight patients, three had their tumors shrink enough to be called a "partial response." More data will come at the meeting.
Nomura analyst Ian Somaiya projected before Incyte's data were released that they might not meet investors' high expectations, and that weakness out of Wednesday could present a buying opportunity heading into the second half of the year.
—By CNBC's Meg Tirrell.