ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2019) 63 OC4.3 | DOI: 10.1530/endoabs.63.OC4.3

Prognostic impact of microscopic extrathyroidal extension (mETE) on recurrence-free survival in patients with papillary thyroid carcinoma (PTC)

Nadia Bouzehouane1,2, Pascal Roy3, Myriam Decaussin-Petrucci4, Mireille Bertholon-Grégoire2, Chantal Bully2,5, Agnès Perrin1,2, Françoise Borson-Chazot1 & Claire Bournaud2

1CHU LYON EST, fédération d’endocrinologie, LYON, France; 2CHU LYON EST, centre de médecine nucléaire, LYON, France; 3CHU LYON, service de biostatistiques, LYON, France; 4CHU LYON SUD, centre d’anatomopathologie, LYON, France; 5Groupe hospitalier Les Portes du Sud, service d’endocrinologie, Vénissieux, France.

Background/objective: mETE has shown no effect on survival, and the 8th edition of the AJCC classification no longer considers mETE in the pT3 definition. Therefore, tumors with mETE below 40 mm are now staged pT1/pT2. However, controversy remains regarding mETE impact on disease recurrence. This study assessed the risk of recurrence of PTC patients previously classified as pT3 because of mETE, compared to PTC patients staged pT1-pT2.

Methods: Monocentric retrospective analysis of prospective database of patients treated by total thyroidectomy and radioactive iodine (RAI) from 1998 to June 2013. All patients had available data on pathology report, uni or multifocal PTC <40 mm, with or without mETE, with or without lymph node involvement (LNI) and at least 5 years of follow-up. mETE was defined as extra-capsular invasion without skeletal muscle involvement. The primary outcome, recurrence free survival (RFS), was defined as the time between initial surgery and recurrence treatment. Follow-up of recurrence-free patients was censored after 5 years. In univariate analyses, the 5-years RFS (with standard error) curves were estimated using the Kaplan Meier estimator and compared using the Log-rank test. Multivariate modelling was performed fitting the proportional hazard Cox model. The candidate prognostic factors were: mETE (presence/absence), LNI (N0-Nx, N1a, N1b), aggressive pathological type (Yes/No), margin resection involvement (R1/R0), pathological tumor size in mm (<=10, ]10; 20], ]20, 40]) and advanced age (>55 years).

Results: The overall 5-years RFS was 80.2% (2.3%). In univariate analyses, the 5-years RFS was 62.4% (5.0%) for tumors with mETE and 88.1% (2.2%) for tumors without (P<0.001). The 5-years RFS were 88.8% (2.1%), 76.6% (6.2%) and 25.0% (7.7%) in N0-Nx, N1a and N1b tumors respectively (P<0.001). The 5-years RFS was 37.7% (17.1%) in aggressive pathological types and 81.4% (2.3%) in others (P<0.001). It was 60.0% (12.6%) in R1 tumors, and 81.3% (2.3%) in R0 tumors (P=0.048). Neither advanced age (P=0.125) nor tumor size (P=0.890) were significantly associated with prognosis. In multivariate analysis, mETE (P=0.002) and LNI (P<0.001) were independent prognostic factors, whereas neither aggressive pathological type (P=0.440) nor resection completeness (0.776) were significantly associated with prognosis. In this model, mETE was associated with a hazard ratio of 2.55 (95% CI 1.48–4.40), and N1a and N1b tumors with hazard ratios of 1.67 (95% CI 0.81–3.46) and 8.94 (95% CI 4.92–16.26) respectively, without interaction between mETE and LNI (P=0.205).

Conclusion: These results suggest that mETE is a pejorative factor in recurrence risk, regardless of LNI.