The significance of unrecognized histological high‐risk features on response to therapy in papillary thyroid carcinoma measuring 1–4 cm: implications for completion thyroidectomy following lobectomy

Background Although lobectomy is an alternative to total thyroidectomy (TT) for 1-4cm papillary thyroid carcinoma (PTC) without high-risk features (HRFs) like aggressive histology, vascular invasion, lymphovascular invasion (LVI), microscopic extrathyroidal extension, positive margin, nodal metastasis >5mm and multifocality, these HRFs are not recognized until after surgery. Therefore, the chance of completion TT being required following lobectomy might be high. We evaluated the frequency of unrecognized HRFs and how they affected the response to therapy following TT and radioiodine (RAI). Methods Altogether 1513 patients were analyzed. Only 1-4cm PTCs without recognizable HRFs were included. For response-to-therapy evaluation, only patients who had TT and post-RAI stimulated thyroglobulin were analyzed. Patients without an excellent response were defined as having “incomplete response”. A multivariate analysis for incomplete response was done. Results Of the 600 patients eligible for lobectomy, 257 (42.8%) had ≥1 unrecognized histological HRF before surgery. The prevalence of unrecognized HRFs was similar between 1-2cm and >2-4cm PTCs (p=0.393). Of the 330 patients eligible for response-to-therapy evaluation, 260 (78.8%) had an excellent response while 70 (21.2%) had an incomplete response. LVI was the only independent unrecognized HRF for incomplete response (p=0.021). Conclusions The prevalence of unrecognized histological HRFs under the current recommendations is relatively high among 1-4cm PTCs. Among the unrecognized histological HRFs, LVI was the only one which independently associated with an incomplete response (i.e. posing an increased risk of persistent/recurrent disease after curative surgery). These findings may have implications for patients who undergo lobectomy for 1-4cm PTCs with no clinically recognizable HRFs under the current recommendations. This article is protected by copyright. All rights reserved.