Abstract
BackgroundIn patients with differentiated thyroid cancer (DTC), tumor burden of persistent disease (PD) is a variable that could affect therapy efficiency. Our aim was to assess its correlation with the 2015 American Thyroid Association (ATA) risk-stratification system, and its impact on response to initial therapy and outcome.MethodsThis retrospective cohort study included 618 consecutive DTC patients referred for postoperative radioiodine (RAI) treatment. Patients were risk-stratified using the 2015 ATA guidelines according to postoperative data, before RAI treatment. Tumor burden of PD was classified into three categories, i.e. very small-, small- and large-volume PD. Very small-volume PD was defined by the presence of abnormal foci on post-RAI scintigraphy with SPECT/CT or 18FDG PET/CT without identifiable lesions on anatomic imaging. Small- and large-volume PD were defined by lesions with a largest size < 10 or ≥ 10 mm respectively.ResultsPD was evidenced in 107 patients (17%). Mean follow-up for patients with PD was 7 ± 3 years. The percentage of large-volume PD increased with the ATA risk (18, 56 and 89% in low-, intermediate- and high-risk patients, respectively, p < 0.0001). There was a significant trend for a decrease in excellent response rate from the very small-, small- to large-volume PD groups at 9–12 months after initial therapy (71, 20 and 7%, respectively; p = 0.01) and at last follow-up visit (75, 28 and 16%, respectively; p = 0.04). On multivariate analysis, age ≥ 45 years, distant and/or thyroid bed disease, small-volume or large-volume tumor burden and 18FDG-positive PD were independent risk factors for indeterminate or incomplete response at last follow-up visit.ConclusionsThe tumor burden of PD correlates with the ATA risk-stratification, affects the response to initial therapy and is an independent predictor of residual disease after a mean 7-yr follow-up. This variable might be taken into account in addition to the postoperative ATA risk-stratification to refine outcome prognostication after initial treatment.
Highlights
In patients with differentiated thyroid cancer (DTC), tumor burden of persistent disease (PD) is a variable that could affect therapy efficiency
In patients with differentiated thyroid cancer (DTC), the risk-stratification system described in the 2015 American Thyroid Association (ATA) guidelines is a useful tool to predict the likelihood of postoperative persistent disease (PD), the response to initial therapy and the long-term outcome [1]
There was a significant trend for a decrease in excellent response rate from the very small, small- to the large-volume PD groups at 9–12 months after initial therapy (71, 20 and 7%, respectively; p = 0.01) and at last follow-up visit (75, 28 and 16%, respectively; p = 0.04) (Fig. 3)
Summary
In patients with differentiated thyroid cancer (DTC), tumor burden of persistent disease (PD) is a variable that could affect therapy efficiency. In patients with differentiated thyroid cancer (DTC), the risk-stratification system described in the 2015 American Thyroid Association (ATA) guidelines is a useful tool to predict the likelihood of postoperative persistent disease (PD), the response to initial therapy (i.e. surgery ± radioiodine [RAI] treatment) and the long-term outcome [1]. Alone or in combination with previous characteristics, notably RAI-avidity, the tumor burden of PD is another variable that can affect treatment efficiency and prognosis This has been shown in studies, sometimes old and using lowresolution imaging methods, focusing on patients with distant metastases [2, 8]. No studies have specified the prognostic role of tumor burden, estimated using high-resolution imaging techniques, both in the setting of distant metastases and lymph-node disease
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