ASCO: Lilly's abemaciclib vs. Pfizer's Ibrance? Too early to make a call, analysts say

Eli Lilly's abemaciclib, if approved, will go up against Pfizer blockbuster Ibrance and Novartis newcomer Kisqali in the CDK 4/6 market.

Investors are champing at the bit for data that will help them determine how Eli Lilly’s candidate abemaciclib stacks up against its in-class rivals—particularly Pfizer’s fast-growing Ibrance—in the efficacy department. But analysts say they’ll have to keep waiting.

On Wednesday, Lilly revealed in an ASCO abstract for its Monarch 2 breast cancer study that a combination of abemaciclib and AstraZeneca’s faslodex had posted median progression-free survival of 16.4 months with a hazard ratio of 0.55, topping placebo-plus-Faslodex’s 9.3-month survival benefit.

While Leerink Partners analyst Seamus Fernandez acknowledged that the data was “seemingly less robust” than the 0.46 hazard ratio Ibrance put up in Pfizer’s Paloma-3 study, it’s not really a fair comparison, he wrote in a note to clients. “Different patient populations and a major difference in the performance of the control group” make measuring the two trials side-by-side difficult, he wrote, and investors may have to wait for full results of another Lilly study—dubbed Monarch 3—to get a better picture of how abemaciclib stacks up.

Evercore ISI analyst Umer Raffat agreed, writing to his clients that “it’s impossible to compare hazard ratios when the trial populations (and the median in the comparator arm) are so different.”

One thing Raffat does think it’s fair to look at, though? The two meds’ tolerability profiles. Lilly’s candidate comes along with a high rate of diarrhea—86.4%, compared with 24.7% for the placebo group—and while the Indianapolis drugmaker says the side effect is “quite manageable with a dose reduction” and OTC remedy loperamide, Raffat pointed out that “in a head-to-head vs. Pfizer, this tolerability metric stands out nonetheless.”

He’s not the only one who thinks so. Last month, Bernstein’s Tim Anderson wrote in a research note that diarrhea could prove particularly burdensome in a drug patients will take for either many months in the metastatic setting or a couple of years in the adjuvant setting.

“Even if low-grade—may influence physician/patient choice adversely,” he wrote. “It is not the kind of differentiation a manufacturer seeks.”

Besides Ibrance, Lilly will have Novartis’ Kisqali to go up against if abemaciclib snags its regulatory go-ahead. The Swiss pharma giant won its FDA OK in March and undercut Ibrance on price to help Kisqali compete with the Pfizer blockbuster.

Leerink’s Fernandez, though, still forecasts Ibrance “taking the lion’s share of the global CDK 4/6” market, he wrote, a market he expects to be worth about $8.8 billion by 2026. He sees abemaciclib, on the other hand, “only achieving ~$1.5 billion sales” that year.