OBJECTIVES: Much progress has been made over the last 10 years with regard to risk estimation in non-medullary differentiated thyroid cancer with risk of recurrence systems and response to therapy re-evaluation approaches being used to augment initial risk estimates obtained using standard anatomic staging systems. Furthermore, risk stratification is being increasingly viewed as an active, evolving, dynamic process that requires re-evaluation during follow-up rather than a single static risk estimate predicted by initial staging. As with differentiated thyroid cancer, multiple clinico-pathologic factors have been demonstrated to correlate with the risk of disease specific mortality, risk of death, likelihood of disease progression, likelihood of cure with initial therapy, and likelihood of cure with additional therapy in medullary thyroid cancer. MATERIALS AND METHODS: In this review, we re-examine the clinically important initial risk factors in medullary thyroid cancer and then re-evaluate how some of these risk factors can be used to alter risk estimates over time as they reflect the response to therapy and the clinical course of the disease. RESULTS AND CONCLUSIONS: We demonstrate that the same response to therapy nomenclature that we have proposed and validated in differentiated thyroid cancer (excellent response, biochemical incomplete response, structural incomplete response, indeterminant response) can be easily applied to medullary cancer and used to guide on-going clinical management.
