An Innovative Approach to Target Lesion Progression in the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1: The Enaworu 25 mm Nadir Rule

The Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 remains the benchmark for evaluating tumour response within clinical trials and oncological practice. It defines disease progression in target lesions as a ≥20% increase in the sum of the longest diameters (SLD), accompanied by an additional absolute increase of ≥5 mm from the nadir. While these dual criteria enhance diagnostic accuracy, their simultaneous application poses several challenges, including the complexity of lesion tracking and potential ambiguity in assessing progression for smaller target lesions. This study presents Enaworu's 25 mm nadir rule, a novel and standardised approach designed to streamline the assessment of target lesion progression. According to this rule, lesions with a nadir of less than 25 mm progress based solely on an absolute increase of 5 mm, whereas lesions with a nadir of 25 mm or more will progress based solely on a 20% increase from the nadir, thereby eliminating the necessity of applying both criteria concurrently. A simulated dataset comprising 1,000 patients, with nadir tumour sizes varying from 0.03 mm to 69.96 mm, was employed to compare progression classification under RECIST 1.1 and the 25 mm nadir rule. The results indicated identical classification outcomes, with 255 patients (25.5%) satisfying the progression criteria under both methodologies. The simplified rule maintained diagnostic accuracy while alleviating administrative burdens and enhancing clarity. The Enaworu's 25 mm nadir rule constitutes a practical refinement of RECIST 1.1, optimising workflow efficiency, reducing ambiguity, and ensuring consistency within clinical and research settings.