The RECIST criteria compared to conventional response evaluation after peptide receptor radionuclide therapy in patients with neuroendocrine neoplasms.

Objective: The Response Evaluation Criteria In Solid Tumors (RECIST) is the most used radiological method for evaluating response after peptide receptor radionuclide therapy (PRRT) in patients with neuroendocrine tumors. This method may give too positive estimates of response in slow growing tumors as it allows a substantial increase in tumor size before patients are classified as having progressive disease. We wanted to compare RECIST with a conventional method in routine use for estimating treatment effect based on defining any unequivocal increase in size of tumor load as progressive disease. We also wanted to investigate whether any differences had clinical implications.

Methods: Patients treated with Lutetium-DOTA-octreotate having at least one follow-up radiological response evaluation were included. Radiological examinations were retrospectively evaluated by RECIST and compared to the radiological evaluations performed at regular follow-up examinations.

Results: Seventy-nine patients were included, 33 (42%) were women, median age 65 years. The primary tumors was located in the small intestine in 35 (44%) and the in the pancreas in 27 (34%) of the patients. Indication for treatment was progressive disease in 71 (90%) patients. Based on RECIST, 67 (85%) patients had objective response or stable disease as best effect versus 59 (75%) patients based on the conventional method (p < 0.001). Median progression free survival was 33 months estimated by RECIST and 28 months estimated with the conventional method (p < 0.001). Eight (10%) patients received tumor-targeted therapy due to progressive disease based on the conventional method while still having stable disease according to RECIST.

Conclusion: Response evaluation after PRRT with RECIST gave more positive estimates for treatment effects compared to a method where any equivocal change in tumor load was regarded as significant. These differences had clinical implications.