Introduction:
Thyroid malignancy is the fifth most common in women worldwide and it is expected to become the second most common malignancy in women and the ninth most common in men by 20301. The incidence of thyroid cancers has been rising over the past few decades. Unlike most head and neck cancers, the presence of distant metastasis (DM) does not preclude curative intent treatment and surgical interventions are common in metastatic disease. DM has an adverse impact on survival and lends considerable morbidity to the patient. Based on the histopathology, thyroid cancers are divided into various subtypes which include differentiated thyroid carcinoma (DTC), medullary and anaplastic thyroid carcinomas. DTCs are derived from thyrocytes, express the sodium transporter and represent 90% of all thyroid cancers and the terminology encompasses papillary thyroid cancer, follicular carcinoma and poorly differentiated thyroid cancers2.
Genetic determinants of clinical behaviour in DTC are being investigated and find applications in the assessment of the risk of malignancy in indeterminate thyroid nodules3 .Notable among these markers has been theBRAFV600E mutation present in 45-59% of papillary thyroid cancer and associated with a higher incidence of extra thyroidal extension, nodal metastasis, refractoriness to RAI treatment and decreased survival4.
Four percent of all patients are diagnosed with or develop distant metastasis. Metastasis develops in 7-15% of patients following thyroid surgery for DTC5. Poorly differentiated thyroid cancers account for 5-10% of all thyroid cancers and the mean survival after diagnosis is 3.2 years6. Bone metastasis have been observed to occur in 2-13% of patients diagnosed with differentiated thyroid cancers. In thyroid cancer, the overall 10 year survival had been declined to 13-21% in the presence bone metastasis7.
Skeletal survey with whole body bone scan, CT/MRI and whole body MRI in patients with spinal cord involvement is warranted whenever there is a suspicion of metastasis. Biopsy from the metastatic site may be required to confirm the histology8.
I131 therapy is the first choice of treatment for papillary and follicular thyroid cancers with distant metastasis, unless they lose the ability to trap iodine9. RAI (Radioactive iodine) therapy has shown to be effective in improving the disease free survival in patients diagnosed with locally advanced or metastatic diseases10.
According to the guidelines published by the American Thyroid Association (ATA), complete removal of bony metastasis has been seen to exert a beneficial effect on survival and it is recommended particularly in younger patients with spinal metastases with neurological deficits11. Hence, completely resectable lesion of bony metastases should be attempted wherever feasible12. Lung metastases respond well to radioactive iodine therapy than any other organ metastases but surgical resection of the lung is undertaken only in selected patients, especially with anatomically limited disease13.
Tyrosine kinase inhibitors are effective and promising drugs for the treatment of poorly differentiated thyroid cancers14. Newer treatment options to treat the locally recurrent and metastatic progressive differentiated thyroid cancers include small molecule oral multi-targeted kinase inhibitors, namely Vandetanib and Sorafenib. Sorafenib works on VEGFR (Vascular endothelial growth factor) 1, 2, and 3 and PDGFR (Platelet derived growth factor).
The role and administration of external beam radiation therapy (EBRT) is not well characterized in differentiated thyroid cancers due to the lack of homogeneity of protocols and conflicting outcomes. In a study done by Lin et al and Benker et al15. They showed that EBRT is not routinely recommended in PTC as there is no significant improvement in overall survival. In fact the higher survival is observed in patients who did not receive EBRT. Despite these drawbacks, in some studies administration of EBRT has improved loco-regional control in invasive disease, unresectable/gross residual tumours and in disease resistant to RAI therapy16.
Unlike cancer at other head and neck sites, patients with metastatic DTC frequently undergo surgery during the course of their protracted treatment. There is no available data on the clinical characteristics and patterns of surgical care received by this rare subset of patients leading us to conduct this study.