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Z.E. Labby



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    MO09 - Mesothelioma I (ID 120)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track:
    • Presentations: 1
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      MO09.10 - Volumetric Response Classification Criteria in Mesothelioma (ID 3302)

      17:10 - 17:15  |  Author(s): Z.E. Labby

      • Abstract
      • Presentation
      • Slides

      Background
      Tumor response criteria provide a framework for therapeutic decisions and clinical trials management in oncology. The standard response classification categories (partial response (PR), stable disease (SD), and progressive disease (PD)) were defined by the Response Evaluation Criteria in Solid Tumors (RECIST) guidelines based on relative changes in linear measurements of tumor diameter on computed tomography (CT) scans. An increase in linear dimension of at least 20% is categorized as PD, a decrease in linear dimension of at least 30% is categorized as PR, and a change in linear dimension not great enough to exceed either of these thresholds is categorized as SD. With improvements in imaging technology and enhancements in computer algorithms, the extraction of tumor volume from CT scans has become more practical. The possibility that tumor volume may eventually become the preferred tumor measurement metric rather than linear dimension necessitates the development of volumetric response criteria. Although extrapolation of the RECIST response criteria to volume is straightforward for spherical nodules, tumors as non-spherical as mesothelioma likely will require unique volumetric response criteria.

      Methods
      A semi-automated computerized method was used to determine the mesothelioma tumor volume from CT scans (baseline and all available follow-up scans) retrospectively collected from 70 patients undergoing standard-of-care chemotherapy. Relative changes in tumor volume from baseline were categorized as PR, SD, or PD based on different combinations of percent change thresholds. Overall patient survival was correlated with best response using Harrell’s C statistic. The response criteria for PD and PR were each varied in 1% increments to obtain optimized classification criteria.

      Results
      The process that systematically evaluated various combinations of response criteria identified an increase in tumor volume of at least 58% and a decrease in tumor volume of at least 17% for PD and PR, respectively, as the criteria that were best correlated with patient survival. These criteria yielded a C statistic of 0.76, where a C statistic value of 1.0 would indicate perfect separation of response groups with respect to subsequent survival times. This result may be compared with the C statistic value of 0.61 obtained when volumetric response criteria extrapolated directly from the RECIST criteria (+73% for PD and -66% for PR) were applied to this cohort.

      Conclusion
      The evolution toward volumetric assessment of tumor burden and response to therapy necessitates the derivation and validation of volume-specific tumor response criteria to distinguish among PR, SD, and PD. The present study motivates such response criteria for mesothelioma and indicates that mesothelioma volumetric response criteria differ substantively from a simplistic extension of the RECIST criteria to three dimensions. Future prospective studies will be required to validate these criteria.

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