Cancer drug sales are on track to eclipse the $200 billion mark early in the next decade, thanks to an innovation bonanza that's transformed oncology into the fastest-growing segment across the entire pharmaceutical industry. Specifically, a recent report by EvaluatePharma estimated that global cancer drug sales will rise at a blistering compound annual growth rate of 12% over the next five years. 

With this double-digit growth trend in mind, we asked three of our Motley Fool contributors which cancer treatment stocks they think are worth buying this month. They picked Geron (NASDAQ:GERN), AbbVie (NYSE:ABBV), and Exelixis (NASDAQ:EXEL). Here's why. 

Cancerous cells floating in plasma.

Image source: Getty Images.

A path forward

George Budwell (Geron): Small-cap cancer companies normally aren't even worth considering as investing vehicles. Developing cancer treatments is prohibitively expensive after all. Geron, however, isn't your typical small-cap cancer play.

The brief rundown is that Geron is developing a first-in-class telomerase inhibitor, imetelstat, for patients afflicted with a blood-based malignancy known as lower risk myelodysplastic syndromes (MDS). Per the company's latest update, the drug's pivotal trial for MDS should commence by the middle of this year. So, depending on how quickly enrollment goes, Geron might be able to file for imetelstat's regulatory approval as early as mid-2021. 

Why is Geron worth a deeper dive? Imetelstat's MDS indication represents  an enormous commercial opportunity for the company. While the entrance of potential competitors like Acceleron Pharma and Celgene's luspatercept has muddied the waters from a commercial standpoint, Geron's management still believes that imetelstat could generate sales in excess of $500 million in the MDS setting. That's a sizable payday for a company with a sub-$340 million cap at the time of writing. 

What's the risk? With less than $182 million remaining in cash, Geron is probably going to have to raise capital at some point during imetelstat's late-stage development. The bright side is that Geron's share price has been bolting higher heading into the start of imetelstat's late-stage MDS trial, and this upward trend should continue based on the magnitude of this commercial opportunity. Therefore, risk-tolerant investors might to take a flier on this deeply undervalued cancer stock this month. 

A growing oncology franchise

Keith Speights (AbbVie): Yes, AbbVie is best known for immunology rather than oncology. That's understandable for a company that claims the world's top-selling drug, Humira, which treats a wide range of autoimmune diseases. But AbbVie is steadily becoming a force to be reckoned with in cancer treatment.

The company's No. 2 product, Imbruvica, is already a major success. AbbVie thinks the drug will generate peak annual sales of around $7 billion in the future. Imbruvica is already more than halfway there, raking in nearly $3.6 billion last year. AbbVie also has a fast-rising star with leukemia drug Venclexta. 

When asked at the Cowen Healthcare Conference in March what investors are missing about AbbVie, the company's president, Michael Severino, listed the strength of AbbVie's early-stage pipeline near the top of the list. Several promising cancer drugs are in that early-stage pipeline, and Severino expects solid progress for these drugs in the next few years. 

Of course, we have to work immunology into any conversation about AbbVie. Although Humira faces biosimilar competition in Europe, the drug remains strong in the U.S. and will likely continue to dominate for several more years. In the meantime, AbbVie expects approvals this year for two new drugs that could take the baton from Humira: risankizumab and upadacitinib.

AbbVie currently trades at only 8.5 times expected earnings. With a dividend yield north of 5% on top of this bargain valuation, I think AbbVie is a great cancer treatment stock to buy in April.

The top value stock among cancer drug developers

Sean Williams (Exelixis): Although big pharma is often viewed as the smartest way for investors to take advantage of novel cancer treatments, my preference among cancer stocks has been the same for years: midcap biotech Exelixis.

Admittedly, Exelixis isn't particularly diversified, which is usually a red flag for pharma and biotech investors. But Exelixis' bread-and-butter drug has delivered multiple label expansions, has additional indication opportunities, and has made Exelixis one of the cheapest growth stocks you can buy in the entire healthcare sector.

Exelixis' Cabometyx was first approved in April 2016, following positive data from the Meteor trial, as a second-line treatment for patients with advanced renal cell carcinoma (RCC). It was the first therapy to deliver a "trifecta" in treating advanced RCC patients. In other words, it provided a statistically significant improvement in objective response rate, progression-free survival, and median overall survival.

In December 2017, following impressive data in the midstage Cabosun study, Cabometyx's label was expanded to include first-line treatment for advanced RCC patients. Rather than trailing Bristol-Myers Squibb's (NYSE:BMY) immunotherapy Opdivo, which it did in second-line RCC, Cabometyx beat Opdivo to the punch in first-line RCC.

And most recently, Cabometyx got the green light from the Food and Drug Administration in patients with previously treated hepatocellular carcinoma (HCC) following strong data in the phase 3 Celestial trial. Both indications (RCC and HCC) may offer more than $1 billion in peak annual sales.

Furthermore, Exelixis is working together with its biggest RCC competitor, Bristol-Myers, on a possible combination therapy in first-line RCC. The CheckMate 9ER trial should read out soon, and if it winds up blowing Pfizer's (NYSE:PFE) Sutent out of the water (Sutent was the standard of care before Cabometyx came along), Exelixis could secure itself a larger share of first-line RCC, even if sharing with Bristol-Myers.

All told, Exelixis is forecast to nearly double sales from $854 million to $1.6 billion between 2018 and 2022, while doubling earnings per share from $1.05 to $2.06 between 2019 and 2022. That's a compound annual sales growth rate of at least 17% and a price earnings-to-growth (PEG) ratio of less than 0.5. For added context, a PEG ratio below 1 is typically considered to undervalued. Exelixis is probably the top value among cancer stocks. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.