Affibody Accelerates Phase 1 Study with ABY-271 Following Initial Patient Data

Affibody said the Trial Review Committee recommended advancing its first-in-human Phase I radioligand therapy ABY-271 (a lutetium-177-labelled Affibody® molecule targeting HER2) to part B after part A data showed tumor targeting with a favorable safety, tolerability, dosimetry and biodistribution profile, notably low kidney and critical-organ uptake; part A enrolled up to six patients and part B will evaluate higher radioactivity levels and additional protein doses in 15 randomized patients. The company will submit a protocol amendment to the EMA to accelerate the transition, with part B expected to start in H1 2026 and initial results anticipated in H2 2026. These early clinical readouts—which reportedly mirror preclinical dosimetry predictions—de-risk the ABY-271 program, reinforce the Affibody platform’s potential for next-generation targeted RLTs and represent a near-term development catalyst for the company.

Analysis

Affibody’s Trial Review Committee recommended advancing the first-in-human Phase I radioligand therapy ABY-271 to part B after review of data from the initial cohort, citing favorable safety, tolerability, dosimetry and biodistribution with demonstrable tumor targeting and notably low kidney and critical-organ uptake. ABY-271 is an Affibody® molecule labeled with lutetium-177 targeting HER2-positive metastatic breast cancer; the TRC finding that early clinical biodistribution mirrors preclinical dosimetry predictions directly supports dose escalation plans.

The study is an open-label, two-stage, randomized Phase I trial with part A evaluating up to six sequential patients and part B planned to randomize 15 patients to higher radioactivity levels and additional protein mass doses. Affibody will submit a protocol amendment to the EMA to accelerate the move to part B, which the company expects to start in H1 2026 with initial part B results anticipated in H2 2026, creating clear near-term clinical milestones.

The data materially de-risk ABY-271 relative to preclinical uncertainty, particularly because low renal uptake is a common safety constraint for RLTs, and the outcome reinforces the broader Affibody platform narrative. Important residual risks remain: small sample size in part A limits generalizability, regulatory review of the amendment and part B tolerability at higher radioactivity are open variables, and the company’s own disclosure emphasizes forward-looking uncertainties.

Key Decisions for Investors

• Monitor the EMA protocol amendment filing and the transition to Part B targeted for H1 2026 and the initial Part B readouts expected in H2 2026 as primary near-term catalysts
• Maintain modest, risk-adjusted exposure or use option strategies until Part B confirms safety and dosimetry in the larger randomized cohort of 15 patients, given the small sample size in Part A
• If Part B confirms low renal uptake and tolerability at escalated activity, consider increasing exposure because the results would materially de-risk ABY-271 and validate the Affibody platform; otherwise be prepared to reduce exposure given clinical and regulatory uncertainty