Two big reasons for the immunotherapy combo approach to cancer treatment? Drug resistance and side effects that come along with older treatments. And though checkpoint inhibitors may be the stars of today's treatment show, previously disappointing cancer vaccines are playing a resurgent role.

Though cancer vaccines have fallen short in clinical trials in recent years, the global market for these products—as crucial pieces of immunotherapy regimens—will likely grow to $7.5 billion in 2022 from $2.5 billion in 2015. That's a compound annual growth rate of nearly 17%, a new report from GBI Research predicts.

A 2015 report by Infiniti Research predicted a higher growth rate of more than 27% through 2019.

Whitepaper Download Reducing the Complexity and Costs of Channel Planning and Logistics How can you make the process of bringing your product to market less complex while also reducing costs? This Whitepaper identifies opportunities to simplify channel strategies for biopharma companies, their customers and patients. Discover how you can deliver savings and innovation to your business. Download for Free

Why is GBI Research so optimistic about cancer vaccines? First, more than 1,200 products are under development, and they make up almost 17% of the entire oncology pipeline. That's the largest of any therapy area, analyst Adam Bradbury said in a statement.

Plus, cancer R&D as a whole is growing rapidly, as a recent report by BioPharm Insight shows. Counting only studies initiated by contract research organizations, 827 cancer trials started in the third quarter of this year, up from 671 for the same period last year.

The new report by GBI Research suggests that new CAR-T immunotherapies from Novartis (tisagenlecleucel-T) and Kite Pharma (KTE-C19) will reach blockbuster status by 2022, if approved.

“[I]t is thought that cancer vaccines will contribute substantially to the treatment landscape for leukemia, lymphoma and myeloma during the forecast period, as expected approvals such as tisagenlecleucel-T will provide much-needed treatment options for refractory blood cancers,” Bradbury added.

For now, Merck and its Gardasil franchise have outpaced other Big Pharma companies in the cancer vaccine market, albeit indirectly. The company’s protective shot against human papillomavirus, which can cause cervical, anal, and head and neck cancers, is the only cancer-fighting vaccine that achieved blockbuster revenue in 2015, the report says. Now that GlaxoSmithKline's Cervarix has exited the U.S. market, Gardasil is almost guaranteed even larger sales.

An overall urgency for new cancer treatments is also contributing to the rise in demand for oncology vaccines. The World Health Organization estimates that about 8.2 million people died from cancer in 2012, and it expects new cases of cancer could increase at a rate of 70% over the next two decades as populations age.

The cutting-edge nature of cancer vaccine technology also means that products have years to go with patent protection, which will keep branded sales coming. Even the first FDA-approved therapeutic cancer vaccine—Dendreon’s 2010 launch Provenge, now owned by Valeant—still has a ways to go before its patent expiration date.

Checkpoint inhibitors such as Merck’s Keytruda, which take the “brakes” off the immune system so that it can recognize and attack cancer cells, are currently dominating the immuno-therapy market, Bradbury acknowledged. But the combo treatment approach leaves plenty of room for complementary treatments, he said: "[G]iven cancer vaccines often have more favorable safety profiles than immune checkpoint inhibitors, they may be promising candidates for combination therapy in future, which could substantially enhance sales.”

Companies are already testing the PD-1 checkpoint inhibitors, including Keytruda, with vaccine add-ons. For example, Merck recently partnered with Genexine to test Keytruda with the latter's cancer vaccine, GX-188E, in HPV-induced cancers. Other such partnerships can be found between Bristol-Myers Squibb and Bavarian Nordic, and AstraZeneca and Inovio.