Background: Although survival rate in papillary thyroid cancer (PTC) is high, the risk of persistence and recurrence together with the dramatic rise in its incidence cannot be overemphasized. Filipinos are considered to be at greater risk for negative outcomes. A paradigm shift in the management of PTC introduces re-stratification based on response to therapy which was reported to have better correlation with long-term outcome. The study aimed to identify predictors of incomplete response after thyroidectomy and radioiodine therapy among patients with PTC. The results of the study may have important implications in our understanding of the disease process allowing more aggressive treatment and monitoring of certain subgroups of patients.
Methodology: Retrospective review of 225 patients with PTC (59% ATA low risk, 30 % ATA intermediate risk and 11% ATA high risk) who underwent thyroidectomy and radioiodine therapy was performed. Thirteen variables were considered (age, gender, histopathological variant, stage, extent of disease, MACIS score, AMES score, primary tumour size, lymph node, lymphovascular invasion, bilaterality, multifocality and preoperative TSH level). Logistic regression analysis using Backward Wald algorithm was used to identify independent predictors of incomplete response to therapy after 24 months.
Results: Of the 225 patients, 69 (31%) had incomplete response. Biochemical and structural (predominantly thyroid bed, lung and bone) incomplete response was observed in 6 and 63 patients, respectively. Incomplete response was documented in 8, 54 and 92% of low-, intermediate- and high-risk patients based on ATA recommendation. Incomplete response was significantly dependent on gender, lymph node involvement and location, extent of malignancy and multifocality taking into account the size of concurrent tumours (p < 0.05). The model was found to have high sensitivity (71%) and specificity (96%).
Conclusion: A significant fraction of PTC patients experienced incomplete response to therapy. Our data suggest that male gender, lateral or mediastinal lymph node involvement, class III extent of disease by De Groot and multifocality with concurrent tumour or tumours more than 1 cm are major predictors of incomplete response. Not all predictors of recurrence and mortality are consistent predictors of treatment response which may be equally important in a disease with low mortality but significant morbidity like PTC.
Keywords: Incomplete response; Papillary thyroid cancer; Predictors.