Structural doubling time predicts overall survival in patients with medullary thyroid cancer in patients with rapidly progressive metastatic medullary thyroid cancer treated with molecular targeted therapies.

PURPOSE To evaluate the impact of structural disease progression of metastatic lesions after initial surgery on overall survival (OS) of patients presenting with metastatic MTC. We used tumor volume doubling time as a marker of structural disease progression and aimed to correlate the average structural tumor doubling time (midDT) with OS in MTC patients after initial surgery. METHODS In this retrospective study, we examined the clinical characteristics, average tumor volume doubling times of neck, lung and liver metastasis and disease specific survival of patients with metastatic medullary thyroid cancer Results: Tumor growth is constant in medullary thyroid cancer metastasis, irrespective of location of the metastasis. The median correlation coefficent (r) and the coefficent of determination (r2) were similar in lung metastasis (r= 0.91, r2 = 0.95 ), and liver metastasis ( r= 0.88, r2=0.94 ) and comparable in neck metastasis ( r= 0.73, r2 = 0.85). Patients with metastatic medullary thyroid cancer with a midDT ≤ 1 year have a worse prognosis than those with higher midDT (p = 0.002). Those with midDT ≤ 1 year had a median OS of 11.1 years (95% confidence interval of 7.4-14.8 years). In contrast, patients with midDT 1-3 years had a median OS of 16.5 years (95% confidence interval of 10.3-22.6 years). All patients with midDT > 3 survived by the end of the follow up period. Preliminary results suggest that measurement of midDT can predict response to molecular targeted therapies. CONCLUSION In conclusion, tumor volume doubling time is a strong predictor of overall survival in patients with recurrent or metastatic medullary thyroid cancer, can be used as a marker of MTC progression, and potentially can help select patients who may benefit from molecular targeted therapy.