Rethinking tumor response: Is RECIST categorization accurate?

Volumetric analysis of breast cancer liver metastasis using CT may provide a more accurate reflection of locoregional treatment response than Response Evaluation Criteria in Solid Tumors (RECIST) categorization, according to a study published online May 13 in Academic Radiology.

Authors Adeel R. Seyal, MD, of Northwestern Memorial Hospital in Chicago, and colleagues noted that while RECIST is a commonly used tool for assessing treatment response, it’s limited by wide, nonflexible response categories and a one-dimensional focus on a lesion’s maximal diameter. In contrast, volumetric analysis of lesions can quantify tumor growth from changes in 3D volumes, and tumor growth kinetics can be determined before appreciable change in the lesion’s size.

“Because of advances in imaging technology and image analysis software, changes in tumor burden can be reliably assessed by whole tumor volume rather than 1D and 2D measurements,” wrote Seyal and colleagues. “By incorporating the tumor volume and time interval between image acquisitions, volumetric growth rate of liver metastasis or change in tumor volume accounting for time interval between scans can be calculated and used for the assessment of response to treatment.”

To compare RECIST with volumetric analysis, the authors conducted a retrospective study featuring 34 chemorefractory breast cancer liver metastases in 21 patients who were treated with yttrium-90. Pre- and posttreatment CT provided measures of tumor growth kinetics. Lesions with a reciprocal of doubling time (RDT) below the range for stable disease were classified as either partial or complete response, while RDT values above the range for stable disease indicated progressive disease.

The results revealed a number of conflicts between RECIST categorization and response based on volumetric analysis. Twenty metastases had growth rates indicating response, but objective classification of response according to RECIST was seen in only six of these. Progressive disease was observed in eight lesions, though RECIST only classified one of these eight as progressive. In the 27 lesions classified as stable by RECIST, growth kinetics indicated partial response in 14 and progressive disease in eight.

“Growth kinetics may reflect response more precisely than RECIST in breast cancer liver metastases treated with locoregional therapy,” wrote the authors.