2 Under-the-Radar Biotech Stocks Worth Buying for the Long Term

Vertex Pharmaceuticals (NASDAQ: VRTX) and Mirum Pharmaceuticals (NASDAQ: MIRM) are two biotech stocks that share the same blueprint. They are focusing on rare diseases with highly unmet medical needs and are using their successful therapies to broaden their platforms.

Vertex has built its financial foundation on its dominance in cystic fibrosis (CF) therapies. Mirum is seeking to widen its platform beyond rare cholestatic liver diseases.

So far this year, Vertex's shares are down more than 2% and Mirum's are up more than 20%. I believe each of these under-the-radar biotech companies is worth buying. Here are three reasons why I like each stock:

Image source: Getty Images.

Mirum is showing explosive revenue growth

Mirum has successfully commercialized Livmarli, which is seeing rapid uptake for rare liver diseases such as Alagille syndrome and progressive familial intrahepatic cholestasis (PFIC). In 2025, the company reported revenue of $521.3 million, up 54%, with Livmarli responsible for $360 million, an increase of 69% over 2024.

The company is continuing to add indications for Livmarli. It also has two other therapies approved by the U.S. Food and Drug Administration (FDA) to treat liver and bile acid diseases: Cholbam for bile-acid synthesis disorders and Ctexli for cerebrotendinous xanthomatosis, a rare genetic bile acid metabolism disorder.

In 2026, the company forecasts product sales of $630 million to $650 million, up 22.7% at the midpoint. It is also edging toward profitability, reporting an annual earnings per share (EPS) loss of $0.45, compared with $1.85 in 2024.

It has a strong pipeline ready to pop

The company is entering a high-reward period with four potentially registrational readouts expected over the next 18 months. Key data is expected from the volixibat Vistas study to treat primary sclerosing cholangitis in the second quarter and the Azure-1 and Azure-4 studies for brelovitug to treat chronic hepatitis delta virus (HDV) in the second half of the year. Positive results here could significantly expand Mirum's addressable market.

The purchase of Bluejay Therapeutics is a game changer

Mirum concluded its $820 million purchase of Bluejay Therapeutics in January, primarily to add brelovitug to its pipeline. The drug holds Breakthrough Therapy status from the FDA and PRIME designation from the European Medicines Agency. These regulatory labels highlight its potential to treat HDV, a condition with no currently approved therapies in the United States.

The clinical stakes are high: HDV is an aggressive disease, with more than half of those diagnosed expected to die from liver-related complications within a decade. With roughly 15 million to 20 million patients worldwide, the demand for an effective treatment is critical. Mirum estimates that successfully addressing this unmet need could generate more than $750 million in annual revenue.

The company has a built-in advantage in marketing the drug, if approved, because the hepatologists and transplant centers that Mirum's sales staff already visits for Alagille syndrome and PFIC are the same specialists who treat HDV.

Vertex has expanded its moat in cystic fibrosis care

Cystic fibrosis is a genetic disorder that affects the lungs, pancreas, and other organs. It affects roughly 112,000 people worldwide, according to Vertex.

The company just received FDA approval on April 1 to expand label extensions for CF therapies Trikafta and Alyftrek, making them available to 95% of all U.S. patients with CF. The expansion targets any variant of the CFTR protein, meaning that the company's CF tandem will be able to restore CFTR function and provide clinical benefit to patients regardless of where in the CFTR protein a variant is located.

The label expansion solidifies Vertex's near monopoly on CF therapies.

The company is stronger than it ever was financially

Vertex reported record annual revenue of $12 billion in 2025, up 9%, led mainly by its CF therapies. In 2026, it said it expects sales of $12.95 billion to $13.1 billion, up 8% at the midpoint, with non-CF therapies accounting for $500 million or more. Even more impressively, annual EPS in 2025 was $15.32, compared with a loss of $2.08 in 2024. Over the past five years, it has increased annual revenue by 58% and annual EPS by 70%.

Its extension beyond CF care

The company's shares have declined because the growth of its non-CF therapies revenue has been underwhelming. However, there is plenty of reason for optimism for non-opioid pain reliever Journavx as well as the continued growth of CRISPR-gene editing therapy Casgevy, used to treat severe sickle cell anemia and beta thalassemia, two rare blood diseases.

Beyond those two, the company has a potential blockbuster in its pipeline, povetacicept to treat IgA nephropathy (IgAN), a rare form of kidney disease. The drug showed positive Phase 3 interim data in March, and the company is on track to complete a rolling Biologics License Application filing for potential accelerated approval in the first half of the year.

Plenty of reasons to like both stocks

Mirum, by adding a second major drug to its sales bag, significantly increases the return on investment for its existing commercial infrastructure. It also broadens the company's technological platform by adding a monoclonal antibody (biologic).

Even after its Bluebird purchase, the company has $391 million in cash and investments, which should allow it to fund its research and development expansion without the pressure to sell stock. The company is only a year or two away from being consistently profitable.

Vertex is already profitable and has $12.3 billion in cash to maintain its CF therapy dominance while growing its portfolio in pain management and kidney disease. By diversifying beyond its core niche, Vertex offers a rare combination of monopoly-like stability and high-ceiling biotech growth.

James Halley has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Mirum Pharmaceuticals and Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.