Radiopharmaceuticals in Phase 3: What BMS' RayzeBio Deal Teaches Us

When a Phase 3 Success Still Raises Questions

A Phase 3 result is considered the gold standard in biotechnology. After years of preclinical work, early-phase trials and regulatory alignment, the third clinical phase delivers the decisive evidence for or against approval. That is precisely why Phase 3 data are the single most important share-price driver for biotech companies — and simultaneously the most dangerous moment for unprepared investors.

The case of Bristol Myers Squibb (BMS) and its $4.1 billion acquisition of RayzeBio illustrates this dilemma in its purest form: the Phase 3 programme in radiopharmaceuticals achieved a positive primary endpoint — which sounds, on the surface, like a clear-cut victory. Yet a subgroup treated with a higher dose failed to meet its endpoint. The overall picture is therefore more nuanced than the headline suggests. For investors in biotech small caps, there is a fundamental lesson to be drawn.

Radiopharmaceuticals: A Growth Field With Complex Physics

Radiopharmaceuticals — also known as targeted radioligand therapies — combine a biological carrier (for example a peptide or an antibody) with a radioactive isotope. The principle: the biological carrier locates the tumour; the isotope destroys it from within. The approach is considered promising because it is more targeted than conventional chemotherapy and can limit systemic side effects.

The segment has gained considerable importance in recent years. Novartis, for instance, has demonstrated with Lutathera (lutetium-177) and Pluvicto (also lutetium-177, for prostate cancer) that approval-grade efficacy data in this field are achievable. These successes triggered a wave of enthusiasm around the entire radiopharmaceuticals segment — and significantly pushed up acquisition prices for small-cap companies operating in this space.

RayzeBio was precisely one of those small-cap companies: a clinically staged biotech focused on actinium-based compounds — that is, alpha emitters rather than the more commonly used beta emitters. Alpha emitters are considered physically more potent but also harder to dose. This characteristic explains why the dosing question became so central to the BMS programme.

Primary Endpoint vs. Subgroup: Why the Distinction Matters

This is the real lesson for investors. A clinical trial programme defines, before it begins, a primary endpoint — the main hypothesis that must be statistically demonstrated for the trial to be considered a success. Alongside it sit secondary endpoints and, sometimes, pre-specified subgroup analyses, for instance for particular dose levels or patient populations.

When the primary endpoint is met, that is the decisive regulatory step towards filing for approval. But when a cohort within the trial — in this case the high-dose group — fails to meet its own endpoint, follow-on questions arise: does the therapeutic principle work only within a specific dose window? Which dose will form the basis of the approval submission? How will the FDA or EMA weigh the mixed signals?

In this specific case, that means: BMS invested $4.1 billion in RayzeBio and receives a positive signal — but not a clean data package. The regulatory dialogue with the FDA will determine which dose is approved and whether requirements for further studies apply. This extends the path to market and increases uncertainty about the true commercial value of the acquisition.

What This Means for Biotech Small Caps and Their Valuations

For investors in biotech small caps — companies with market capitalisations below $2 billion that often generate no revenue — the case is instructive on several levels.

First: milestone payments are not guarantees. When a biotech small cap enters a licensing deal or an acquisition with staged payments, many of those payments are tied to the achievement of clinical or regulatory milestones. A "Phase 3 success" does not automatically trigger all milestone payments — because if subgroup failures delay or constrain the approval process, payouts can be deferred or may not materialise at all.

Second: the high-dose problem in radiopharmaceuticals is not an isolated case. Alpha emitters such as actinium-225 are regarded as particularly potent because they combine very short range with high energy. But those same properties make dose-finding difficult. Preclinical models and early-phase trials do not always accurately reflect the toxicity of alpha emitters. When a high-dose cohort fails in Phase 3, this is often not evidence of a failed therapeutic concept — but rather of the difficulty in precisely defining the therapeutic window.

Third: acquisition prices in the radiopharmaceuticals segment have risen sharply on the back of Novartis' successes. This means that small caps in this space are frequently valued at a substantial premium to future success — before Phase 3 data are even available. When those data then come in mixed, the valuation correction can be significant, even if the primary endpoint was formally met.

Radiopharmaceuticals as a Sector: Structural Potential Requiring Patient Capital

Setting aside the individual RayzeBio case, the structural argument for radiopharmaceuticals remains intact. The global burden of cancer is rising, targeted therapies are gaining ground over non-specific systemic treatments, and nuclear medicine infrastructure in hospitals is gradually being expanded. These are genuine trends — but they are not short-term share-price catalysts.

For small-cap investors, this means: even if a company in this segment possesses a valid technology, the timelines from early clinical stages to commercialisation are long and capital-intensive. A typical biotech with no revenue burns through substantial sums each month (burn rate). The remaining cash balance divided by this burn rate gives the so-called cash runway — the period of time before new capital is required. If that runway is too short, capital increases that dilute existing shareholders become likely, or, in the worst case, the company may face liquidation.

A total loss of capital — the complete loss of money invested — is a realistic scenario for biotech small caps without stable revenues, not merely a theoretical warning. Even a positive trial cannot fully eliminate this risk if the commercial environment, the regulatory outlook or the financing situation are unfavourable.

Key Takeaways from the RayzeBio Case

The BMS/RayzeBio case is a textbook example of how clinical data are rarely straightforward — and how the gap between "Phase 3 success" and "a clean data set" is very much priced into share values. Anyone investing in biotech small caps or following acquisition deals in the sector would do well to ask the following questions:

• What exactly is the primary endpoint — and does it measure clinically meaningful outcome parameters such as overall survival, or merely surrogate markers?
• Which subgroups were pre-specified, and what happens if one of them fails?
• How many milestone payments in an acquisition or licensing deal depend on regulatory decisions that come only after the Phase 3 topline readout?
• How long is the company's cash runway if the approval process is delayed?

These questions cannot always be answered fully from public company disclosures — but asking them is what distinguishes informed market observation from blind narrative investing. The radiopharmaceuticals segment remains scientifically fascinating. Whether individual small caps within it achieve commercial success hinges on details that lie well beneath the headline.

Key Terms at a Glance

Primary Endpoint

The pre-specified main objective of a clinical trial. Only when this endpoint is statistically demonstrated is the trial considered successful — regardless of other results.

Secondary Endpoint

Additional measurement objectives in a trial (e.g. quality of life, biomarkers) that provide supplementary insights but do not form the basis for approval.

Subgroup Analysis

An evaluation of trial data for a specific patient group (e.g. by dose level or genetic profile). Pre-specified subgroups carry greater regulatory weight than post-hoc ones.

Topline Data

The initial, summary announcement of trial results, before full analysis is complete. Topline data do not constitute a complete data set and may still change following detailed review.

Radiopharmaceutical

A drug that combines a biological carrier (e.g. antibody, peptide) with a radioactive isotope to deliver targeted radiation to tumour cells.

Cash Runway

The length of time a company can sustain operations with its current cash reserves before new capital is required. Calculation: cash balance ÷ monthly burn rate.

Dilution

When a company issues new shares (e.g. via a capital increase), the stake held by existing shareholders in the company decreases — their percentage ownership becomes smaller.

Milestone Payment

A payment agreed within a licensing or acquisition contract that only becomes due when a defined event occurs (e.g. FDA approval, positive Phase 3 readout).

⚠️ Important notice: This article is for informational and educational purposes only. It does not constitute investment advice, a recommendation, or a solicitation to buy or sell any security. Investments in small-cap exploration and mining companies carry a high risk, including the potential total loss of capital. Before making any investment decision, consult a registered financial advisor and conduct your own analysis. Aktienatlas-Redaktion is not responsible for decisions taken based on the content published here.

Educational content only, not investment advice. Small caps are highly speculative and total loss is possible.