What are the RECIST (Response Evaluation Criteria In Solid Tumors) criteria for evaluating treatment response in non-small cell lung cancer (NSCLC)?

RECIST Criteria for NSCLC

The standard for evaluating treatment response in non-small cell lung cancer (NSCLC) is RECIST 1.1 criteria, which should be used after two to three cycles of chemotherapy using the same initial radiographic investigation that demonstrated tumor lesions. 1

RECIST 1.1 Criteria Overview

RECIST (Response Evaluation Criteria In Solid Tumors) 1.1 provides standardized measurements for assessing tumor response to therapy. The key components include:

Target Lesion Assessment

• Complete Response (CR): Complete disappearance of all target lesions
• Partial Response (PR): Decrease ≥30% in the sum of the greatest diameters of target lesions
• Stable Disease (SD): Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD
• Progressive Disease (PD): Increase ≥20% in the sum of the greatest diameters or appearance of new lesions 1

Measurement Methodology

• Unidimensional measurements (longest diameter) are used rather than bidimensional measurements used in older WHO criteria
• Maximum of 5 target lesions per organ with an overall maximum of 10 lesions (reduced from previous versions) 1
• For lymph nodes, the short axis measurement is used, with complete response defined as reduction to <10mm in short axis 1

Implementation in NSCLC

Timing of Evaluation

• Response evaluation should be performed after 2-3 cycles of chemotherapy 1
• For patients who responded to first-line therapy and maintain good performance status, follow-up should be considered every 6-12 weeks to allow for early initiation of second-line therapy 1

Imaging Modalities

• Use the same initial radiographic investigation that demonstrated tumor lesions
• Follow-up with PET is not routinely recommended due to its high sensitivity but relatively low specificity 1
• Contrast-enhanced CT scan of the chest and upper abdomen is typically used 1

Special Considerations

EGFR/ALK TKI Treatment

• The adequacy of RECIST in evaluating response to EGFR or ALK tyrosine kinase inhibitors (TKIs) in genetically driven NSCLC is debatable 1
• Studies show that RECIST 1.1 provides highly concordant response assessment with a decreased number of target lesions compared with RECIST 1.0 in EGFR mutation-positive NSCLC patients treated with TKIs 2
• However, some research suggests that new CT response criteria incorporating morphological characteristics may better predict survival in EGFR-TKI treated patients 3

Immunotherapy Response

• For immune checkpoint inhibitor therapy, while RECIST criteria should be used, immune-related response criteria (irRECIST, iRECIST, imRECIST) may have a role in the overall assessment of therapy 1
• These immune-related criteria account for the possibility of pseudoprogression and delayed responses

Clinical Impact of RECIST Assessment

• Objective response by RECIST criteria is a significant predictor for better survival in advanced and metastatic NSCLC treated with first-line or salvage chemotherapy 1
• Disease control rate (response plus stable disease) has been shown to correlate with survival in some studies 1
• Some research suggests that a 10% tumor shrinkage (rather than the standard 30% for PR) might be a more indicative threshold for efficacy evaluation in NSCLC patients treated with chemotherapy plus targeted agents 4

Practical Application

1. Identify and measure target lesions at baseline (maximum 5 per organ, total 10)
2. Document non-target lesions
3. Perform follow-up imaging after 2-3 cycles of therapy using the same imaging modality
4. Measure target lesions and calculate the sum of diameters
5. Compare with baseline measurements to determine response category
6. Assess non-target lesions and note any new lesions
7. Determine overall response based on target, non-target, and new lesion assessment

Common Pitfalls to Avoid

• Using different imaging modalities for baseline and follow-up assessments
• Inconsistent measurement techniques between evaluations
• Failing to account for special considerations with targeted therapies or immunotherapies
• Over-reliance on PET for response assessment due to its high sensitivity but lower specificity
• Not considering clinical benefit in cases where RECIST criteria may not fully capture treatment response

By following these standardized RECIST 1.1 criteria, clinicians can more accurately assess treatment response in NSCLC patients and make appropriate therapeutic decisions.