Response assessment classification in patients with advanced renal cell carcinoma treated on clinical trials

The objective of the current study was to evaluate the effect on response assessment classification in patients with metastatic renal cell carcinoma (RCC) using unidimensional (Response Evaluation Criteria in Solid Tumors) and bidimensional (World Health Organization) criteria, including or excluding measurements of the primary renal tumor and using a new index to compensate for the disproportionate effect of large renal tumors relative to their metastases.

Fifty-three imaging studies involving a total of 44 patients with metastatic RCC who were treated on clinical trials of interferon-alpha analogue and/or thalidomide were reviewed retrospectively. The best overall response assessment and progression free survival were calculated with both unidimensional and bidimensional tumor measurements. Patients were then stratified into two groups: patients with primary renal tumors in situ and patients who underwent resection of their primary renal tumors. The best overall response and the time to disease progression were calculated based on the sum of measurements (conventional methodology), both including and excluding the primary tumor. A new method of response assessment, the 'normalized lesion index', which equalizes the differences in tumor size for an individual patient, was evaluated and compared with the conventional response assessment.

There was an 11% disagreement rate in the best overall response assessment between unidimensional and bidimensional measurements. The time to progression was 9.2 months measured unidimensionally, compared with 6.4 months assessed bidimensionally. In the group of patients who had primary renal tumors in situ, using the conventional sum of measurements method, the apparent time to progression was an average of 4.2 months longer compared with measurements that did not include the primary renal tumor. The use of the normalized lesion index method resulted in an improved concordance in best overall response assessments and similar time to progression assessments when the primary renal tumor was included compared with patients who did not have primary renal tumors in situ.

The use of unidimensional measurements in RCC therapy assessment results in significantly different time to progression classification compared with the use of bidimensional measurements. Response assessment classification in patients with RCC is affected by the exclusion or inclusion of measurements of the primary renal tumor. The normalized lesion index warrants further study in assessing response in patients with metastatic RCC and other solid tumor malignancies that often show substantial differences in sizes of measurable lesions.