LATERAL NECK DISSECTION FOR AGGRESSIVE VARIANTS OF WELL-DIFFERENTIATED THYROID CANCER

Well-differentiated thyroid cancer (WDTC) is characterized by favorable disease course and excellent survival. However, some histologic subtypes, known as aggressive histologic variants (AHVs), present a more aggressive behavior than conventional WDTC. The aim of this study was to evaluate the pattern of nodal involvement and factors influencing prognosis in N1b patients with AHVs. A multicentric retrospective analysis of patients who underwent therapeutic lateral neck dissection (ND) for WDTC between 1994 and 2015 was accomplished. AHVs included the following subtypes: tall cell, Hürtle cell, diffuse sclerosing, and poorly differentiated papillary thyroid cancer. The study included a total of 352 N1b patients, 40 (11.4%) of whom had AHVs. AHVs present a similar distribution of positive nodes if compared with conventional WDTC. In AHV patients, 5-year overall survival (OS), disease-specific survival (DSS), locoregional control, and metastasis-free survival were 82.2%, 93.6%, 80.3%, and 87.3%, respectively. Advanced age (>55 years) was the only significant factor affecting survival (OS, P<.001; DSS, P = .011) in this group. In the AHV group, there were 9 (22.5%) recurrences; patients with regional recurrence and without distant metastases were effectively treated by surgery. The distribution of positive lymph nodes in case of AHVs is similar to that of conventional WDTC, with only level V at a relatively greater risk of harboring metastases in the former group. Survival outcomes in N1b patients with AHVs remain optimal. Total thyroidectomy, ND, and adjuvant radioiodine administration have been demonstrated to be effective treatments in the setting of AHVs. Abbreviations: AHV = aggressive histologic variant; DOD = died of disease; DSS = disease-specific survival; DSV = diffuse sclerosing variant; ETE = extrathyroidal extension; HCC = Hürthle cell carcinoma; LRC = locoregional control; LVI = lymphovascular invasion; MFS = metastasis-free survival; ND = neck dissection; NED = no evidence of disease; OS = overall survival; PDA = poorly differentiated areas; PTC = papillary thyroid carcinoma; RAI = radioiodine therapy; TCV = tall cell variant; WDTC = well-differentiated thyroid cancer.