What is itRECIST? Intratumoral immunotherapy response evaluation criteria in solid tumors (itRESIST) are an initial set of standardized criteria that is used to capture data and evaluate the efficacy of treatment of solid tumors with intratumoral immunotherapy.

How is itRECIST different from RECIST and iRECIST?

itRECIST has been designed to assess the response as the treatment evolves by monitoring the overall response (non-injected lesions) as well as local response (injected lesions). This differs from RECIST and iRECIST as they only assessed systemic therapy. 

itRECIST follows the RECIST 1.1 guidelines closely for lesion measurement and assessment of baseline tumor burden, and iRECIST guidelines in terms that the response assessment would be refined as data is collected. However, this is with some modifications:

  • Ultrasound may be used to measure some subcutaneous lesions when there are no other lesions available. Use of the same operator and equipment is recommended at all visits.
  • Lesions are classified further to include whether the lesions are injected: Targeted injected lesions, targeted non-injected lesions, non-targeted injected lesions, and non-targeted non-injected lesions.
  • The sum of the longest diameter is calculated using all targeted lesions combined, and separately for targeted injected lesions and targeted non-injected lesions. These are eventually used to assess the local, systemic, and overall response to the treatment.

Source: Goldmacher et al. (2020). Response Criteria for Intratumoral Immunotherapy in Solid Tumors: itRECIST. Journal of Clinical Oncology, 38(23), 2667–2676.