13. Ibrance

Pfizer’s Ibrance grew sales by 9% in 2020 to $5.39 billion. (Pfizer)

Company: Pfizer
2020 sales: $5.39 billion
Diseases: HR-positive, HER2-negative breast cancer

As the first CDK4/6 inhibitor on the market, Pfizer’s Ibrance posted 2020 sales of $5.39 billion, a 9% increase. But its days of big-time growth may be numbered.

Last year, Ibrance missed the marks in two separate trials testing it on top of endocrine therapy after surgery in patients with early HR-positive, HER2-negative breast cancer. They showed that adding the drug couldn’t lengthen the time patients could live without invasive disease returning either in a broader early breast cancer population or in a high-risk subset of patients who still have residual disease after receiving chemotherapy prior to surgery.

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

The flops closed the doors on Ibrance in the adjuvant setting, denying the Pfizer blockbuster a multibillion-dollar market. And perhaps more importantly, the series of failures fuels the hypothesis that Ibrance is an inferior drug to Eli Lilly’s rival CDK inhibitor Verzenio, SVB Leerink analyst Geoffrey Porges wrote in an investor note in October.

In what was hailed as a practice-changing result, Verzenio showed its addition to standard endocrine therapy after surgery significantly cut the risk of cancer recurrence by 25.3% in patients with high-risk HR+/HER2- early breast cancer. Investigators released the phase 3 monarchE trial results at ESMO 2020.

What's more, the adjuvant trial flops might affect Ibrance’s leading position in the existing metastatic setting, Porges suggested. The drug, used in tandem with AstraZeneca’s endocrine therapy Faslodex, previously posted a narrow life-extension failure in metastatic disease from the phase 3 Paloma-3 trial.

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

To back the case for its drug, Pfizer resorted to real-world data showing that adding Ibrance to Novartis’ hormone therapy Femara could cut the risk of death by 34% after two years of treatment based on patient records collected from a Flatiron Health database. But the theory hasn’t been corroborated by a controlled trial as the phase 3 Paloma-2 study has yet to report overall survival data.

Not all analysts agreed that Ibrance’s position in the metastatic market is under threat. The drug’s total CDK market share remains strong at about 86% to 87%, with about 80% of all new scripts still going to it, Pfizer CEO Albert Bourla said at the J.P. Morgan Healthcare Conference in January.

Ibrance was Pfizer's top drug by sales last year, trailing only pneumococcal vaccine Prevnar 13 on the company's sales charts.

13. Ibrance