Hepatic high ratio on whole-body radioiodine scans: a robust prognostic marker in well differentiated thyroid cancer.

[PURPOSE] Radioiodine therapy (RIT) is a well established adjuvant therapy in intermediate and high-risk patients of well differentiated thyroid cancer (WDTC). Diagnostic whole-body radioiodine (WBRI) scans are done to evaluate remnant lesions and metastatic burden. Sometimes, diffuse liver uptake is noted in WBRI scans, even in the absence of liver metastasis. Few studies have assessed the hepatic-thigh ratio (HTR) on WBRI and found its correlation with the functional status of tumour cells and prognostication. We assessed the baseline HTR in WDTC and evaluated the dynamics of HTR in different groups after RIT in the follow-up.

[METHODS] Sixty WDTC patients (30 in metastatic and 30 in nonmetastatic groups) were included in a prospective study. Patients underwent baseline WBRI scans, and RIT was done. Follow-up was conducted at six and 12 months, including biochemical investigations and WBRI. The baseline hepatic-to-thigh ratio (HTR0) was calculated as the average counts per pixel of a region of interest drawn in the right lobe of the liver and the mid-thigh. Correlation analysis of HTR0 and follow-up HTR (HTR1 and HTR2) with tumour markers, liver enzymes, histopathology, and outcome was done.

[RESULTS] The mean ages of patients with and without metastasis were 35.8 and 42.03 years, respectively. There was no significant difference between serum thyroglobulin, serum thyroglobulin antibody (TgAb), age, thyroid-stimulating hormone, and HTR0, HTR1, and HTR2 among nonmetastasis and metastasis groups (P > 0.05). Papillary and follicular carcinomas were noted in 46 and 14, respectively. A complete response was noted in the 31 patients and was associated with the papillary carcinoma and HTR2 < 2.135. HTR2 < 2.135 predicted a complete response with a sensitivity and specificity of 90% and 82%, respectively. Rising HTR in follow-up was associated with incomplete response. HTR1 and HTR2 were higher in follicular carcinoma compared to papillary carcinoma.

[CONCLUSION] HTR0 is unrelated to the disease burden (thyroglobulin and metastasis) and histopathological variant. High HTR0 is associated with poor response and residual disease. Rising HTR in follow-up also signifies the inadequate response to RIT. HTR acts as a supplementary tool to existing risk factors, and thyroglobulin for predicting therapeutic response in DTC.