1. Rituxan

Roche executives previously expected Rituxan to face early biosim competition last year, but now they're guiding for new entrants in the second half of 2019. (Roche)

2018 U.S. sales: $4.29 billion
Disease: Blood cancers, rheumatoid arthritis
Competition expected: Second half of 2019

For the second year in a row, Roche's Rituxan tops the list of drugs expected to face U.S. competition from copycats. Executives with the Swiss cancer specialist had previously said they expected biosimilars in 2018, but those knockoffs never came. Now, the drug will have company when they do: It's expected to be among a trio of Roche blockbusters to face biosimilar rivals in the second half of 2019. 

Rituxan pulled in about $4.29 billion in the U.S. last year, up 4% over 2017—partly in thanks to the absence of those biosimilars. In Europe, Rituxan wasn't so lucky; sales cratered 47% there thanks to competition.

One U.S. biosimilar is now waiting in the wings. Celltrion and Teva scored FDA approval in November for their copycat, called Truxima, but haven’t yet launched. A Teva spokesperson said the biosim launch date is confidential. 

Roche, for its part, hasn't set out specific expectations for Rituxan sales erosion in the U.S. That's because "two obstacles" stand in the way of accurate projections, pharma head Bill Anderson said during the company's fourth-quarter conference call. Biosimilar launch timing is unknown, he said, and there's no way of knowing how quickly they'll be adopted when they do arrive in the U.S.  

“Frankly, there's not lots of precedents to look at on that,” he said of the U.S. biosimilars market. “So I think we've baked in some impact in the second half, and it's not a huge impact because it happens in the second half and there's only so much that can happen.” 

RELATED: Even in worst-case scenario, Roche will grow past biosimilar erosion in the U.S.: executive 

Aside from the Teva and Celltrion partnership that just won its Truxima approval, Amgen, Pfizer and Sandoz are among the biosimilar developers working on their respective programs aimed at Rituxan.  

Rituxan is only one Roche blockbuster facing potential competition this year. The company expects two other big-selling cancer drugs, Avastin and Herceptin, to come under biosim attack in the second half. The trio together generated more than $10 billion in the U.S. last year, and the drugmaker is leaning on new launches such as Ocrevus and Hemlibra to lift its fortunes under the long-anticipated biosimilar erosion. 

1. Rituxan