OP72 – Predictive factors for occult contralateral lateral lymph node metastases (LNM) in N1b Papillary Thyroid Carcinoma (PTC)

      Hartl, Dana1; Bohec, Hélène Diaz1; Badois, Nathalie2; Mamelle, Elisabeth3; Mirgani, Haïtham1; Breuskin, Ingrid1; Leboulleux, Sophie4 1 Department of Head and Neck Oncology, Thyroid Surgery Unit, Gustave Roussy and Paris Sud University, Villejuif, France 2 Otolaryngology Head and Neck Surgery, Curie Institute, Paris, France 3 Otolaryngology Head and Neck Surgery, Hôpital La Pitié Salpétrière, Paris, France 4 Department of Medical Imaging, Endocrine Oncology and Nuclear Medicine, Gustave Roussy and Paris Sud University, Villejuif, France   Background: Therapeutic lateral neck dissection is recommended for N1b PTC, while prophylactic contralateral lateral neck dissection is not, in the absence of data regarding occult contralateral nodes. Objective: We investigated the risk factors for occult LNM in the contralateral lateral neck for N1b patients who had total thyroidectomy, therapeutic central dissection, homo-lateral lateral neck dissection and prophylactic contralateral lateral neck dissection. Methods: This retrospective study enrolled 63 patients treated in comprehensive cancer center between 1997 and 2016. Inclusion criteria were : unilateral PTC confirmed by ultrasound and fine-needle aspiration biopsy,and with homo-lateral lateral metastases. Patients with contralateral lateral metastases or bilateral tumor at diagnosis were excluded. Results: Occult contralateral lateral LNM were found in 23/63 patients (36.5%) and were significantly associated with the number of metastatic nodes in the central compartment ispilateral to the tumor (p=.02) and with microscopic tumor foci in the contralateral thyroid lobe (p=0,017). Using receiver operating characteristic analysis, a cutoff of 5 or more metastatic nodes in the ipsilateral level VI optimized sensitivity and specificity for predicting contralateral lateral nodal metastases, with a sensitivity of 74%, specificity of 65%, positive predictive value of 55%, a negative predictive value of 81% for an overall accuracy of 68%. For 8 or more nodes, specificity was 90%. Conclusion: This study suggests that occult LNM in the contralateral lateral neck can be predicted. Five or more ipsilateral central lymph nodemetastases were correlated with a risk of contralateral lateral lymph node metastasis, as were the presence of microscopic contralateral tumor foci


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