5. Opdivo

Opdivo held on to its U.S. market lead in immuno-oncology last year, but 2019 could be different. (BMS)

5. Opdivo
Company: Bristol-Myers Squibb
2018 U.S. sales: $4.2 billion
Used for: advanced melanoma, non-small cell lung cancer, small cell lung cancer (SCLC), kidney cancer, Hodgkin lymphoma, head and neck cancer, bladder cancer, colorectal cancer, liver cancer

In the U.S. last year, Bristol-Myers Squibb’s Opdivo maintained its lead over Merck & Co.’s Keytruda, despite the latter’s full-court press for new indications—particularly its wins in lung cancer.

Opdivo pulled in $4.24 billion in U.S. sales last year, an impressive 37% increase. But because of Keytruda's new first-line approval, its share in lung cancer is under threat. That's an approval Opdivo doesn't have, and it positions Keytruda to leach away patients that might otherwise use Opdivo in the second-line setting.

Still, Bristol-Myers keeps pushing for new Opdivo uses, and it racked up multiple wins last year. Trials testing Opdivo in rare forms of lung cancer and in neuroendocrine tumors, for example, came up positive.

But for each of those wins, Opdivo suffered even more setbacks in 2018, with a trial failure for treatment of patients whose cancer had returned after one round of platinum-based treatment, and a second trial failure for treatment of SCLC in combination with Yervoy.

Opdivo will also face even more pushback from Keytruda, which secured a nod from the FDA in November for the treatment of hepatocellular carcinoma, a rare liver cancer, and already leads the field in lung cancer treatment.

And thanks to Keytruda's advances, Opdivo's grip on the top I-O slot in the U.S. may not hold in 2019. The Merck drug edged ahead in the first quarter with $1.28 billion in sales, compared with $1.12 billion for Opdivo.

5. Opdivo