Prothena Corp Plc Dossier - Source-backed chat

Prothena Corp Plc

PRTANASDAQ

SectorHealth Care

IndustryBiotechnology

Beta (adjusted)0.11

Intrinsic Value

No headline value published yetWe haven't published a headline intrinsic value for this company yet. Our data-reliability standards weren't met. Method estimates are shown for reference.

Market Price $8.54Price as of 1 Oct 2026

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Market Cap $438.4M

Enterprise Value $150.2M

Shares Outstanding 53.4M diluted

Next Earnings Date9 Nov 2026

All prices and values are periodic snapshots, not live quotes. Source dates are shown for reference.

Thesis

Street consensus, scenarios, merits, risks, and invalidation triggers

AI-assisted

Thesis Summary

Prothena Corporation plc is a late-stage clinical biotechnology company focused on protein dysregulation therapies. Following the major Phase 3 AFFIRM-AL trial failure for its wholly-owned lead candidate birtamimab in May 2025, which led to the discontinuation of the program and subsequent corporate restructuring, Prothena's investment profile has shifted heavily toward its partnered pipeline. The company's near-to-mid-term valuation is anchored by high-profile collaborations with global pharmaceutical giants, including Roche (prasinezumab for Parkinson's disease in Phase 3), Novo Nordisk (coramitug for ATTR-CM in Phase 3), and Bristol Myers Squibb (BMS-986446 for Alzheimer's disease in Phase 2). While these partnerships validate Prothena's scientific platform and offer up to $3 billion in potential aggregate milestones, the primary completion dates for the key Phase 3 programs are distant (expected in 2029). Consequently, the stock is maintained at a Hold rating as investors await more substantial clinical readouts and near-term milestone triggers.

This section is the 12-month view: analyst targets and the probability-weighted scenarios built from them. The intrinsic value at the top of this page answers a different question: what the business is worth today.

Street view · analyst 12-month targets5 analysts · as of 18 Aug 2026

Low · most bearish analyst$8.00

Mean target$21.40

High · most bullish analyst$36.00

Our research · scenarios, merits, risks, and invalidation triggersResearch as of 19 Jun 2026

Scenarios · 12-month scenario targetsAnchored at research date

Bear CaseDownside scenario

$8.0015%

The bear case involves Bristol Myers Squibb opting not to advance PRX019, resulting in no milestone payment by year-end 2026. Additionally, any safety concerns (such as ARIA incidence in Alzheimer's programs) or delays in the Phase 3 trials for prasinezumab or coramitug would severely depress investor sentiment. Continued cash burn without near-term commercial revenues could force dilutive capital raises in late 2026 or 2027.

Base CaseCentral scenario

$21.4060%

Matches the consensus mean

The base case assumes Prothena continues to execute on its partnered pipeline without major clinical setbacks. The company is expected to end 2026 with approximately $273 million in cash, supported by the $50 million milestone received from Novo Nordisk in Q1 2026. Near-term stock performance will likely remain range-bound, dictated by progress updates at medical conferences and the execution of its up to $100 million share repurchase program.

Bull CaseUpside scenario

$36.0025%

In the bull case, Bristol Myers Squibb decides to advance PRX019 into Phase 2 development by year-end 2026, triggering a $55 million milestone payment. Concurrently, Novo Nordisk rapidly meets Phase 3 enrollment targets for coramitug, unlocking further clinical milestones. Positive early readouts or accelerated timelines from the Phase 2 TargetTau-1 trial for BMS-986446 in 1H 2027 could reignite speculative interest in Prothena's neurodegenerative pipeline, driving significant multiple expansion.

Scenarios are anchored to street consensus at the research date, with our probabilities and rationale.

Key Investment Merits

Strong cash position of $330.3 million as of Q1 2026 with zero debt, providing a solid runway.
Deeply validated pipeline through high-value partnerships with Roche, Novo Nordisk, and Bristol Myers Squibb.
Substantial non-dilutive funding potential with up to $3 billion in aggregate future milestone payments plus royalties.
Active capital return program with an authorized share repurchase program of up to $100 million through 2026.

Key Investment Risks

High reliance on partner execution and long development timelines, with key Phase 3 readouts not expected until 2029.
History of late-stage clinical failures, notably the birtamimab Phase 3 AFFIRM-AL failure in May 2025 and the NEOD001 halt in 2018.
Pre-commercial status with no sustainable product revenues, making financial stability highly dependent on binary milestone events.
Intense competition in the neurodegenerative and amyloidosis spaces from larger, fully-integrated pharmaceutical companies.

Thesis Invalidation Triggers

Decision by Bristol Myers Squibb not to advance PRX019 into Phase 2 development by year-end 2026.
Unexpected clinical holds, safety signals, or termination of the Phase 3 trials for prasinezumab (Roche) or coramitug (Novo Nordisk).
Failure to achieve projected year-end 2026 cash balance of approximately $273 million due to elevated operational burn.

All scenarios are estimates and subject to change. Past performance is not indicative of future results.

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Explore this dossier

ValuationIntrinsic value, the six-method breakdown, peer medians, and your assumptions sandbox.Financial SnapshotRevenue, profitability, returns, balance sheet, dividends, and the filing-level detail.Qualitative AnalysisBusiness overview, strategic initiatives, and mergers, acquisitions & partnerships.Outlook & Key DatesForward estimates, reporting calendar, and the monitoring framework.