You better have all your spring-cleaning out of the way to make room for a slate of clinical trial readouts and FDA decisions coming up soon. Before April's finished, all of these biopharmaceutical stocks could swoon or soar depending on how upcoming events play out.

Company (Stock Symbol) Market Capitalization Key Asset
GW Pharmaceuticals (NASDAQ:GWPH) $5.1 billion Epidiolex
FibroGen (NASDAQ:FGEN) $4.8 billion pamrevlumab
Heron Therapeutics (NASDAQ:HRTX) $2 billion HTX-011
Assembly Biosciences (NASDAQ:ASMB) $503 million ABI-H0731

Data source: Yahoo! Finance.

GW Pharmaceuticals: Expanding Epidiolex

This is the first company to earn FDA approval for a cannabis-derived drug. Epidiolex is a cannabidiol (CBD) tincture that GW Pharmaceuticals launched last year for two treatment-resistant forms of early onset epilepsy.

GW Pharmaceuticals is running a phase 3 trial for patients with uncontrollable seizures caused by tuberous sclerosis complex (TSC). Before the end of April, we'll know if Epidiolex has a chance to add this third indication, and success could help the stock continue climbing.

The company thinks there are around 35,440 patients eligible for treatment with Epidiolex now. Success with the TSC indication could add another 25,000 patients to its list of potential customers and give the stock a huge boost in the process.

Prescription pills stacked in the shape of an upward-sloping chart.

Image source: Getty Images.

FibroGen: Preventing scars 

This company's anemia treatment, roxadustat, recently earned approval in China for the treatment of patients with kidney-disease-associated anemia. FibroGen will probably submit an application for the same indication in the U.S. in the third quarter, and any day now the company should let us see some data from a second program called pamrevlumab.

FibroGen is expected to announce interim results from a phase 2 trial with pamrevlumab as a treatment for non-ambulatory Duchenne muscular dystrophy (DMD) patients. This experimental injection appears to halt scar tissue formation, also known as fibrosis, in some important places.

Respiratory and cardiac problems are the main cause of mortality among DMD patients. With this in mind, reducing fibrosis that stiffens the heart and lungs should provide a significant survival benefit. Evidence that pamrevlumab works as expected would also boost confidence for phase 3 studies with the candidate in pancreatic cancer and pulmonary fibrosis slated for 2019.

A variety of pills on hundred-dollar bills.

Image source: Getty Images.

Heron Therapeutics: An extended-release anesthetic

Physicians have been using bupivacaine as a local anesthetic since the 1960s. Heron Therapeutics applied the proprietary extended-release technology used for another commercial-stage product to the old favorite, and the new concoction, HTX-011, does a better job for patients after getting their hernias repaired and bunions removed.

In pivotal studies supporting an application still under review, patients injected with HTX-011 reported significantly less pain intensity than those given old-fashioned bupivacaine. Heron Therapeutics can also point to evidence that shows patients injected with HTX-011 were less likely to require opioid rescue medication than patients given the old standard.

There's a large unmet need for nonaddictive post-surgical pain medication, and it won't be long before we find out if Heron's candidate can meet that need. The FDA granted Heron a priority review, and an approval decision is expected on or before April 30, 2019.

A microphone with a classroom in the background.

Image source: Getty Images.

Assembly Biosciences: Best in show?

On April 13, 2019, at the annual meeting of the European Association for the Study of the Liver (EASL), Assembly Biosciences could finally get the attention it's been missing. This clinical-stage biotech is working on a new way to tackle hepatitis B virus (HBV) called ABI-H0731, which could surprise investors who dismissed the program when the company reported phase 1 data last November.

At EASL, Assembly Biosciences is expected to present six-month data from ongoing phase 2 studies with ABI-H0731 and new HBV patients, plus another trial with chronic HBV patients. The association accepted the company's presentation of six-month results as a late-breaker for the main event and labeled it one of several "best in show" submissions.

HBV still requires lifelong treatment in an effort to stop the virus from shutting down patients' livers, and these efforts often fail. There are around 1.5 million Americans living with chronic HBV, and a more effective treatment could easily drive annual sales up to several billion in a few short years. If Assembly presents signs of success, it could send shares of the stock screaming higher.

Not the only big event

An interim look at Assembly's HBV candidate isn't the only biotech catalyst expected to make waves at EASL this month. Some upcoming presentations from Alnylam Pharmaceuticals and Intercept Pharmaceuticals will probably soak up most of the attention this month, which is fine -- just as long as you don't ignore these under-the-radar 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.