The First Standardized PET Response Framework for Neuroendocrine Tumors: The Lancet Oncology | July 2026

Introduction:

Somatostatin receptor (SSTR) PET/CT has become indispensable for diagnosing, staging, and monitoring neuroendocrine tumors (NETs). However, until now, there has been no standardized method for assessing treatment response using SSTR PET imaging. This international consensus introduces the SSTR-PeRForm (Somatostatin Receptor PET Response Framework) to harmonize response assessment.

Why was this guideline needed?

• No standardized PET-based response criteria currently exist for NETs.
• Existing RECIST criteria may not adequately reflect functional changes seen on SSTR PET.
• Variability in PET interpretation limits consistency across clinical practice and research.
• Uniform response criteria are needed for clinical trials and routine patient care.
• Standardized reporting may improve treatment decisions and future research.

Key Recommendations:

• Response assessment should primarily rely on changes in tumor volume of SSTR-expressing lesions rather than SUV-based measurements.
• Partial Response (PR): ≥40% reduction in target lesion volume with no new lesions.
• Progressive Disease (PD): ≥40% increase in target lesion volume or appearance of new lesions.
• Complete Response (CR): Complete disappearance of pathological somatostatin receptor uptake.
• Unconfirmed Progressive Disease (uPD): A new category for equivocal findings requiring repeat imaging before confirming progression.
• SUV measurements alone should not be used to define treatment response.
• Volumetric assessment and identification of new lesions are considered the most clinically relevant imaging parameters.
• The framework is intended for both clinical trials and routine practice, pending prospective validation against survival outcomes.

Clinical Impact:

SSTR-PeRForm is the first internationally endorsed framework for SSTR PET response assessment in NETs. It provides a standardized, practical approach that is expected to improve reporting consistency, treatment monitoring, and the design of future clinical trials.

Bottom Line:

SSTR-PeRForm establishes the first consensus-based PET response criteria for neuroendocrine tumors. By emphasizing volumetric tumor changes and new lesion detection, it lays the foundation for standardized response assessment and future outcome-based validation.