Endocrine Abstracts

Background: Lymph node metastases at histology (pN1) are usual findings in differentiated thyroid cancer (DTC) patients. Their detection has an impact on the extent of surgery, the further treatments after surgery, and on the clinical outcome.

Material and method: We evaluated data of 1332 consecutive DTC patients who performed the first ¹³¹I treatment between January 2010 and September 2012. According to their pN status, they were divided into 2 groups: Nx/N0 and N1. The latter was subdivided in central compartment (N1a) and latero-cervical compartment (N1b) metastases. Clinical outcome, according to 2015-ATA was defined at: post-operative and post-¹³¹I (median time from surgery: 6 months), first evaluation after ¹³¹I (median time from ¹³¹I: 8 months) and last evaluation (median time from ¹³¹I: 83 months).

Results: 1064 (79.9%) patients were in the Nx/N0 and 268 (20.1%) in the N1 group. N1 patients were more frequently males (35.8 vs 27.3%, P <0.01) and younger (median age 40 vs 47, P <0.01). Several histologic features were significantly more frequent (P <0.01) in the N1 group: multifocality (63.4 vs 46.8%), mETE (67.9 vs 24.6%), vascular invasion (28 vs 8.9%) and intermediate ATA-risk (94.8 vs 36.5%). Structural incomplete response (StR) rate was higher in N1 group throughout the follow-up (P < 0.01), although these patients experienced higher ¹³¹I activities over time and more neck re-intervention. Also, N1b (n = 142, 53%) patients, compared to N1a (n = 126, 47%), had more frequently mETE (74.6 vs 59.5%, P <0.01) and vascular invasion (33.1 vs 22.2%, P <0.05) and lower prevalence of histologic thyroiditis (21.1% vs 35.7, P <0.01). Nevertheless, N1b patients experienced higher ¹³¹I activities and more neck re-intervention during the follow-up. StR rate was significantly higher in N1b at post-operative (16.2 vs 6.3%), post-¹³¹I (26.1 vs 8.7%) and at first evaluation after ¹³¹I (24.3 vs 9.6%). Conversely, at the last evaluation, significance was not reached (17.9 vs 10.4%, P = 0.09).

Conclusions: pN1 status is related to more aggressive histologic features in DTC patients. Although more treatments were performed during the follow-up, the N1 patients had a higher StR rate at each time of the follow-up when compared with Nx/N0. Moreover, N1b patients, compared to N1a, experienced more frequent and aggressive treatments during the follow-up but still with a higher persistence of StR.