There has been tremendous progress in the battle against cancer, but it remains the second leading cause of death in the U.S., behind heart disease. That means there is plenty of work left to be done.

So which cancer-focused companies are worth watching? We asked three Motley Fool healthcare contributors to weigh in, and they called out Blueprint Medicines (NASDAQ:BPMC), Halozyme Therapeutics (NASDAQ:HALO), and Merck (NYSE:MRK).

Science microscope looking at sample

Image source: Getty Images.

A map to better cancer drugs

Todd Campbell (Blueprint Medicines): Increasingly, researchers are discovering that our genetic makeup may hold the key to developing better medicines. It's not science fiction, either. The Food and Drug Administration has already approved cancer drugs that target specific genetic markers, and one of those approvals sparked Eli Lilly's $8 billion acquisition of Loxo Oncology earlier this year.

A slate of companies could benefit from this shift in how we treat disease, but Blueprint Medicines is my favorite to buy now.

Like Loxo Oncology, Blueprint Medicines is developing drugs targeting genetic mutations. Its most advanced therapy is avapritinib, a possible treatment for gastrointestinal stromal tumors (GIST) and systemic mastocytosis (SM) that inhibits the protein kinases KIT and PDGFRA. Data from trials in advanced GIST is expected soon that could support a new drug application in June. Trials evaluating avapritinib's use in SM and earlier use in GIST could result in filings for those indications in 2020.

Blueprint is also studying BLU-667, a potential drug for RET-altered lung cancer, medullary thyroid cancer, and other solid-tumor cancers. A filing for BLU-667 could also result in an approval as early as next year.

The results reported on these drugs so far are encouraging, and Blueprint Medicines maintains 100% of the U.S. and EU rights to these therapies, so approvals could be needle-moving. There's no telling if additional data will pan out or if the company will successfully execute on its aggressive timeline, but management's experience suggests investors should give it the benefit of the doubt.

For instance, its CEO was formerly the U.S. president of Algeta, which was acquired by Bayer for $2.9 billion in 2013. Blueprint's chief medical officer formerly ran Novartis' oncology research, and before that, he was a vice president for oncology research at Millennium Pharmaceuticals, which was acquired by Takeda for nearly $9 billion in 2008.

Check out the latest earnings call transcripts for Blueprint Medicines, Halozyme Therapeutics, and Merck.

Big pharma's go-to partner

Brian Feroldi (Halozyme Therapeutics): Halozyme Therapeutics is a small-cap biotech that is focused on cancer, but with an interesting twist. The company is pursuing two business models at the same time to drive growth.

Halozyme's primary business is to partner with big pharma companies to help them make their drugs work better. It accomplishes this with its proprietary ENHANZE technology, which enables drugs to be absorbed by the body more easily. That's a big deal because it allows some drugs to be delivered via injection instead of an arduous infusion.

Halozyme has already established a who's who of big partners, including Roche, Pfizer, Johnson & Johnson, AbbVie, Eli Lilly, and others. Halozyme has already pulled in millions of dollars in milestone payments and royalties from these partnerships.

The company's partnership agreements are enticing on their own, but Halozyme also comes with a lottery ticket. The company has been pumping money into a wholly owned compound called PEGPH20 that holds promise as a treatment in numerous types of cancer. The company is furthest along with its HALO-301 study, which is a phase 3 trial that is testing PEGPH20 with Abraxane from Celgene and gemcitabine as a treatment for pancreatic cancer. Top-line results are due out in the back half of 2019, and if the results look good, then Halozyme's stock will likely soar.

It is certainly a risky stock, but I find comfort in Halozyme's numerous partnerships and its cash-packed balance sheet ($355 million at year-end). Adding in the PEGPH20 lottery ticket makes this a compelling cancer stock for risk-loving investors to get to know.

In-market immunotherapy for multiple cancer types

Chuck Saletta (Merck): There was a time in the not too distant past when treating patients with advanced lung cancer was often ethically questionable because of the pain of treatment and the questionable benefits. With modern immunotherapy from Merck's Keytruda combined with chemotherapy, a test indicated that the death rate from lung cancer dropped in half. That completely changes the conversation to one of hope and a legitimate chance at survival.

Another test indicated that Merck's Keytruda doubled the median survival length of patients with stage III-IV melanoma-type skin cancers that cannot be surgically removed. Other tests show benefits from Keytruda for Hodgkin lymphoma, cervical cancer, bladder cancer, gastric cancer, and other cancers as well.

While Keytruda isn't a universal and sure cure for all cancers, it certainly works wonders for the patients and cancer types it can treat. Even former President Jimmy Carter credits Keytruda for his own success fighting off melanoma.

At least partly on the success of Keytruda, Merck's shares have recently been retesting highs they haven't seen in decades. That raises the question of whether there may really be more room to grow. And on that front, Keytruda's early successes look like they may pave the way for even more areas of treatment. Merck has more than 30 different clinical trials planned or underway around that already approved compound, potentially expanding the scope of the cancers it can treat.

Immunotherapy like Keytruda is proving itself an incredibly valuable tool in the fight against cancer. With a strong compound already on the market, Merck is well positioned to continue to learn and build upon its successes, offering its patients the opportunity to live and its investors the potential to profit.