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Prothena Stock Tumbles 36.8% Year Over Year: What Lies Ahead?
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Key Takeaways
PRTA shares fell 36.8% in a year after birtamimab failed a late-stage study and was discontinued.
Prothena relies on partner revenues as losses widened and earnings missed estimates in four quarters.
PRTA's late-stage progress hinges on partners like Novo Nordisk and Roche, not wholly owned assets.
Shares of Prothena Corporation (PRTA - Free Report) have plunged 36.8% over the past year against the industry’s 19.6% rise.
The decline can be attributed to pipeline setbacks, most notably the failure and subsequent termination of its wholly owned candidate, birtamimab, in a late-stage study.
Image Source: Zacks Investment Research
The company has reported inconsistent earnings over the last four quarters, with results largely reflecting wider losses due to higher research and development expenses and the impact of pipeline setbacks, including the discontinuation of birtamimab.
Prothena’s earnings missed estimates in each of the trailing four quarters, with the average negative surprise being 26.72%.
The company’s top line currently comprises only collaboration revenues from its partner Bristol Myers Squibb (BMY - Free Report) .
Pipeline Setbacks Impact PRTA’s Growth Prospects
In May 2025, Prothena announced the discontinuation of the development of the pipeline candidate, birtamimab, after the AFFIRM-AL study failed to meet its primary endpoint. This removed a near-term value driver.
Birtamimab was a wholly owned potential best-in-class anti-amyloid antibody for the treatment of AL amyloidosis for Prothena.
Its termination significantly reduced near-term catalysts for the stock and redirected the company’s strategic focus toward earlier-stage assets such as PRX012, which remain several years away from potential commercialization.
PRTA announced a 63% workforce reduction in June to streamline operating costs, ensuring continued support for its wholly owned programs, partnered program obligations, and planned business development initiatives.
Progress on PRTA’s Partnered Programs
PRTA’s pipeline progress has been driven largely by partnered assets rather than wholly owned programs.
Prothena’s partner Novo Nordisk (NVO - Free Report) is evaluating coramitug, a potential first-in-class amyloid-depleting antibody, in the phase III CLEOPATTRA program for ATTR cardiomyopathy (ATTR-CM). This represents meaningful late-stage progress within the collaboration portfolio.
Coramitug was initially developed by Prothena and was acquired by Novo Nordisk in July 2021.
The candidate could earn Prothena up to $1.23 billion in development and sales milestones, including $100 million already received, with additional payments tied to phase III enrollment targets. The recently published phase II results support the ongoing phase III study in ATTR-CM patients.
Roche(RHHBY - Free Report) , another partner of PRTA, initiated the phase III PARAISO study on prasinezumab, a potential first-in-class anti-alpha-synuclein antibody for early-stage Parkinson’s disease, underscoring continued commitment to this collaboration and potential future milestones.
Prothena has a worldwide collaboration agreement with RHHBY, under which it has received $135 million to date. The deal includes up to $620 million in additional development and commercial milestone payments, along with royalties in the double-digit to high-teen range on future sales. Prothena also retains an option to co-promote prasinezumab in the United States.
PRTA is also advancing an early-to-mid-stage pipeline of programs for several potential neurological indications with BMY.
In Alzheimer’s disease (AD) research, Bristol Myers Squibb obtained Fast Track designation from the FDA for its anti-tau antibody BMS-986446 (PRX005) and is conducting the phase II TargetTau-1 study in approximately 310 patients with early AD. Primary completion is expected in 2027.
BMS-986446 is a best-in-class anti-tau, MTBR-specific antibody that is being investigated for the potential treatment of AD.
BMY is also conducting a phase I open-label single-dose clinical trial to assess subcutaneous administration. Bristol Myers Squibb is responsible for all development, manufacturing and commercialization.
PRX019, a potential treatment for neurodegenerative diseases, is also being developed in collaboration with BMY.
PRTA has initiated an early-stage first-in-human study on PRX019 to evaluate the safety, tolerability, immunogenicity, and pharmacokinetics of single ascending and multiple doses in healthy adults. The phase I study is expected to be completed in 2026.
While these updates highlight progress in partnered programs, the discontinuation of birtamimab remains a major overhang on the shares.
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Image: Bigstock
Prothena Stock Tumbles 36.8% Year Over Year: What Lies Ahead?
Key Takeaways
Shares of Prothena Corporation (PRTA - Free Report) have plunged 36.8% over the past year against the industry’s 19.6% rise.
The decline can be attributed to pipeline setbacks, most notably the failure and subsequent termination of its wholly owned candidate, birtamimab, in a late-stage study.
Image Source: Zacks Investment Research
The company has reported inconsistent earnings over the last four quarters, with results largely reflecting wider losses due to higher research and development expenses and the impact of pipeline setbacks, including the discontinuation of birtamimab.
Prothena’s earnings missed estimates in each of the trailing four quarters, with the average negative surprise being 26.72%.
The company’s top line currently comprises only collaboration revenues from its partner Bristol Myers Squibb (BMY - Free Report) .
Pipeline Setbacks Impact PRTA’s Growth Prospects
In May 2025, Prothena announced the discontinuation of the development of the pipeline candidate, birtamimab, after the AFFIRM-AL study failed to meet its primary endpoint. This removed a near-term value driver.
Birtamimab was a wholly owned potential best-in-class anti-amyloid antibody for the treatment of AL amyloidosis for Prothena.
Its termination significantly reduced near-term catalysts for the stock and redirected the company’s strategic focus toward earlier-stage assets such as PRX012, which remain several years away from potential commercialization.
PRTA announced a 63% workforce reduction in June to streamline operating costs, ensuring continued support for its wholly owned programs, partnered program obligations, and planned business development initiatives.
Progress on PRTA’s Partnered Programs
PRTA’s pipeline progress has been driven largely by partnered assets rather than wholly owned programs.
Prothena’s partner Novo Nordisk (NVO - Free Report) is evaluating coramitug, a potential first-in-class amyloid-depleting antibody, in the phase III CLEOPATTRA program for ATTR cardiomyopathy (ATTR-CM). This represents meaningful late-stage progress within the collaboration portfolio.
Coramitug was initially developed by Prothena and was acquired by Novo Nordisk in July 2021.
The candidate could earn Prothena up to $1.23 billion in development and sales milestones, including $100 million already received, with additional payments tied to phase III enrollment targets. The recently published phase II results support the ongoing phase III study in ATTR-CM patients.
Roche(RHHBY - Free Report) , another partner of PRTA, initiated the phase III PARAISO study on prasinezumab, a potential first-in-class anti-alpha-synuclein antibody for early-stage Parkinson’s disease, underscoring continued commitment to this collaboration and potential future milestones.
Prothena has a worldwide collaboration agreement with RHHBY, under which it has received $135 million to date. The deal includes up to $620 million in additional development and commercial milestone payments, along with royalties in the double-digit to high-teen range on future sales. Prothena also retains an option to co-promote prasinezumab in the United States.
PRTA is also advancing an early-to-mid-stage pipeline of programs for several potential neurological indications with BMY.
In Alzheimer’s disease (AD) research, Bristol Myers Squibb obtained Fast Track designation from the FDA for its anti-tau antibody BMS-986446 (PRX005) and is conducting the phase II TargetTau-1 study in approximately 310 patients with early AD. Primary completion is expected in 2027.
BMS-986446 is a best-in-class anti-tau, MTBR-specific antibody that is being investigated for the potential treatment of AD.
BMY is also conducting a phase I open-label single-dose clinical trial to assess subcutaneous administration. Bristol Myers Squibb is responsible for all development, manufacturing and commercialization.
PRX019, a potential treatment for neurodegenerative diseases, is also being developed in collaboration with BMY.
PRTA has initiated an early-stage first-in-human study on PRX019 to evaluate the safety, tolerability, immunogenicity, and pharmacokinetics of single ascending and multiple doses in healthy adults. The phase I study is expected to be completed in 2026.
While these updates highlight progress in partnered programs, the discontinuation of birtamimab remains a major overhang on the shares.
Prothena Corporation plc Price
Prothena Corporation plc price | Prothena Corporation plc Quote
PRTA’s Zacks Rank
Prothena currently carries a Zacks Rank #3 (Hold). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.