Prognostic Impact of Focal Poorly Differentiated Areas in Follicular Differentiated Thyroid Cancer: Is It a Distinct Entity from Poorly Differentiated Thyroid Cancer?

Poorly differentiated thyroid cancer (PDC) and especially poorly differentiated areas (PDA) within follicular cell-derived differentiated thyroid cancer are ill-defined clinicopathological entities. We report our experience on their comparative prognostic outcomes This is a retrospective study of 61 patients (PDC = 29; PDA = 32) from Endocrine and Metabolic Surgery Department (2009 to 2017). Clinical and follow-up details are collected and digitally tabulated from departmental database. Gender ratio was M:F = 1:1.3 and 1:1.6. Mean age was 51 ± 12 years (16-76) and 54 ± 10.5 years (36-81) in PDA and PDC, respectively. Mean tumour size (4.6 ± 0.9 cm; 4.9 ± 1.2 cm), extrathyroidal invasion (59%; 73%) and regional lymphadenopathy were 50% and 55% in PDA and PDC, respectively. Total thyroidectomy was possible in 94% of PDA and in only 77% of PDC. Radioiodine ablation was utilised in 65% (PDA); 29% (PDC). With mean follow-up of 64 ± 23.5 months (12-103) in PDA and 37 ± 22 months (6-94) in PDC, nodal recurrence (PDC = 29%; PDA = 22%) and systemic metastasis was 41% in PDC (synchronous = 24%; metachronous = 17%); 19% in PDA (synchronous = 16%; metachronous = 3%). Five-year event-free survival (EFS) and overall survival (OS) was 90% and 93% in PDA, and 42% and 44% in PDC, respectively. Our study shows that PDA is a separate clinicopathological entity with significantly positive prognosis compared to PDC.