5. Ibrance

Product: Ibrance
Generic name: palbociclib
Company: Pfizer
2015 sales: $723 million
2022 sales: $6.01 billion
Current indication: metastatic breast cancer

Ibrance—the first in a new class of CDK 4/6 inhibitors—has romped away since Pfizer launched it in the U.S. in February 2015 as a combination therapy with letrozole for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer that has spread to another part of the body.

The product showed no sign of slowing down in 2016, with first-half sales approaching a whopping $950 million. That growth was fueled by a second approval, in combination with AstraZeneca's Faslodex (fulvestrant), in women whose disease has progressed after hormone therapy. It's a remarkably quick rollout, considering that, at last count, the drug was still only approved in 15 countries, with a regulatory decision in Europe not expected until later this year.

Ibrance has potential rivals hot on its heels, however, with Novartis' ribociclib on the FDA's priority review track toward approval. Eli Lilly is following behind with abemaciclib—claiming advantages in terms of its safety and dosing regimen—but had a setback in August when an interim data analysis in a phase 2 trial showed it had not yet hit its efficacy objectives. That could delay a launch of abemaciclib until 2018.

Meanwhile, Pfizer is spending big to stay ahead of the competition. It is testing Ibrance on no fewer than 38 other cancers as it tries to capitalize on its lead in the market.

5. Ibrance