RECIST criteria in Oncology

RECIST or Response Evaluation Criteria in Solid Tumors is a framework (https://recist.eortc.org/) developed by EORTC, NCI, CCTG and multiple big tech pharmaceutical companies for assessment of tumor progression, mainly for non-operable tumors, but not limited to (this is a very interesting aspect which I will discuss in more detail).

While surgical intervention usually means that the RECIST is no longer applicable as a methodology, but very important, from the moment of surgical intervention. So for a situation of Neoadjuvant chemo or immuno-therapy + surgery, the RECIST may be used for the analysis of Neoadjuvant segment of the treatment, but not to fully estimate the Neoadjuvant effects, as these effects may span more than the moment of surgery.

The RECIST is used in many submissions to the FDA today and is referenced in their Guidance document : https://www.fda.gov/media/71195/download for Approvals of Biologics for Industry, especially in relation to ORR (objective response rate) and CR (complete response) standardized definitions.

These criteria are the foundation, but the foundation is complemented with many aspects which ill discuss later :

• Complete Response (CR) - Disappearance of all target tumor lesions

• Partial Response (PR) - Minus 30% in sum of longest diameters of target lesions

• Stable Disease (SD) - does not comply with either PD or PR or CR

• Progressive disease (PD) - Plus 20% in sum of longest diameters of target lesions

  Source : https://recist.eortc.org/recist-1-1-2/

  But be careful as with the new changes, the PD also needs to comply the criteria of the sum of target lesion longest diameters also having and increase of at least 5mm in absolute value. So its not just a percentage as a criteria but also the absolute value in mm. This was not in some of the previous versions, so make sure to use the latest RECIST version in your studies.

But as you can see there is a term target lesion and the sum of longest diameters of target lesions. It very important to understand that RECIST is not just about the criteria above. The definition of a target lesion is very important.

Also the follow up period is very important. According to RECIST, the optimal follow up periods are 6-8 weeks, but this is not a strict criteria, but rather a guide on what to consider as a default. In studies regarding metastatic tumors, or other fast growing tumors, follow ups could be weekly or even daily.

For slow growing or chronic tumors, the follow up periods could be longer.

The latest version of RECIST is 1.1 https://recist.eortc.org/recist-1-1-2/ and there are multiple version, all important to read. Also there is a RECIST called iRECIST designed specifically for Immuno-therapy in Oncology field https://recist.eortc.org/irecist/.

To simplify your data collection process, you should use the RECIST data collection form : https://recist.eortc.org/wp-content/uploads/sites/4/2020/04/Initial-Measurement-form-RECIST-1.1.pdf

This form contains everything needed to start with the data collection under the RECIST protocol. There you may find overview, description and measurement forms as well as sequence and date data. Multiple such forms are usually needed in Oncology RECIST based studies.