Pfizer's Ibrance kisses early breast cancer hopes goodbye with 2nd study failure

Ibrance
Analysts are split on whether Pfizer's early breast cancer miss, coupled with rival Eli Lilly's adjuvant success, will hurt its share in the metastatic setting. (Pfizer)

After Pfizer’s Ibrance failed a crucial study in HR-positive, HR-negative postsurgery breast cancer patients, the company clung to hope that it could still show a benefit in a high-risk subset of those patients. But new data have officially snuffed out those hopes.

There’s “no saving adjuvant for Ibrance,” SVB Leerink analyst Geoffrey Porges wrote in a Friday note to clients.

In women who still had residual disease after undergoing presurgery chemo, Pfizer’s drug failed to lengthen the time patients could live without invasive disease returning. The phase 3 trial, dubbed Penelope-B, “puts to bed any notion” that Ibrance will ever be an option in early breast cancer patients, Porges wrote.

The news didn’t surprise analysts, who widely expected a flop after Pfizer detailed its failed phase 3 Pallas trial at last month’s European Society for Medical Oncology virtual annual meeting. That study looked at Ibrance in the wider adjuvant group, showing the drug didn't deliver a benefit. In a subgroup breakdown Porges labeled “dismal,” Ibrance showed it didn’t help high-risk patients, either.

RELATED: ESMO: Lilly's Verzenio pressures Pfizer with practice-changing win in early breast cancer

But the Penelope-B stumble did bring a key question into sharper focus: Will its adjuvant showing hurt Ibrance in the metastatic setting, where it currently holds court?

The way Porges sees it, it’s “inevitable that there is some spillover in terms of share of new starts in the metastatic setting,” given that Eli Lilly’s rival drug Verzenio is all lined up for an adjuvant green light after posting practice-changing data at ESMO. Adding the Lilly med to standard endocrine therapy after surgery slashed the risk of cancer recurrence by 25.3% among high-risk patients, results showed.

The Penelope-B miss “further substantiates the hypothesis that Ibrance is an inferior molecule with less effective CDK inhibition than Lilly’s Verzenio,” Porges said.

But RBC Capital Markets’ Randall Stanicky disagreed. “We don’t expect this to impact PFE's leading position in the metastatic setting, which as of today consists of ~79% of the CDK4/6 class,” he wrote of the Penelope-B data in his own Friday note to clients.

Others, including Evercore ISI’s Umer Raffat, were less conclusive. Since the readout from Lilly’s successful adjuvant trial, monarchE, Ibrance hasn’t looked to be ceding its ground. “But we’ll track this dynamic over time,” he noted.

RELATED: ESMO: Pfizer's Ibrance flop in early breast cancer shouldn't hurt metastatic sales, exec says

Pfizer, for its part, has been vocal about the fact that it doesn’t expect to see its metastatic share slip.

“I’ve got to say that all our interactions with thought leaders, through market research with medical oncologists that treat breast cancer, they look at early breast cancer very differently from metastatic,” Andy Schmeltz, global president and general manager of Pfizer's oncology unit, said in an interview ahead of ESMO, adding that “we do not expect any impact on Ibrance’s … positioning or performance in the metastatic setting.”

But in the meantime, with an eye on clawing back a competitive edge, the company will be applying the learnings from its pair of trial misfires to up-and-coming CDK drugs in its pipeline.

“We look forward to continuing to work with our research partners to understand subgroup data and how these could inform the development of our next-generation CDK inhibitors in early breast cancer,” Chris Boshoff, M.D., Ph.D., Pfizer’s chief development officer for oncology, said in a statement.