12. Herceptin

Herceptin won a breast cancer nod alongside Perjeta in June. (Roche)

Company: Roche
2019 sales: $6.08 billion
Projected 2026 sales: $2.08 billion
Projected CAGR: -14%
Used for: HER2-positive breast cancer, stomach cancer

Like Roche's other two top-selling oncology drugs, Avastin and Rituxan, breast cancer med Herceptin faced U.S. biosimilar challengers for the first time in 2019. Unlike Herceptin's portfolio mates, however, Roche may have found a path forward for the blockbuster med as part of a combo therapy. 

Herceptin hit $6.08 billion in sales in 2019, but those peak sales will soon be a thing of the past. Evaluate Pharma forecast that Roche's drug will reach just $2.08 billion in sales in 2026 with copycats on the market. 

But while Herceptin's solo days as one of pharma's top-selling drugs are likely coming to a close, a combination of Herceptin and another Roche drug could keep the therapy relevant for years to come. 

RELATED: Roche wards off Herceptin copycats with new, easy-to-use Perjeta combo product

12. Herceptin