Risk of recurrence in a homogeneously managed pT3-differentiated thyroid carcinoma population

International guidelines for the management of differentiated thyroid cancers are based on the 7th TNM classification: pT3 tumors are defined as differentiated thyroid cancers (DTCs) measuring more than 4 cm in their greatest dimension that are limited to the thyroid or any tumor with minimal extrathyroidal extension (ETE; sternothyroid muscle or perithyroid soft tissues). Differences in clinicohistological features and prognosis among patients with pT3 tumors remain controversial, and studies regarding pT3 subgroups are lacking.

To analyze the prognosis of four subgroups of pT3 DTCs (papillary, PTC; or follicular, FTC).

The data of patients who underwent surgery for pT3 DTC between 1978 and 2015 in a surgical department specialized in endocrine surgery were reviewed. Patients were classified into four groups as follows: the pT3a (≤ 10 mm with ETE), pT3b (10-40 mm with ETE), pT3c (> 40 mm without ETE), and pT3d groups (> 40 mm with ETE). Recurrence-free survival (RFS) was analyzed using the Kaplan-Meier method.

One thousand eighty-eight patients with pT3 DTC were included, of whom 311 (29%) had pT3a; 548 (50%), pT3b; 165 (15%), pT3c; and 64 (6%), pT3d. For the 916 patients with lymph node (LN) dissection, metastatic LNs were more frequent in the pT3b and pT3d groups (61 and 61%, respectively) than in the other groups (44% pT3a and 10% pT3c; p < 0.001). During the median follow-up period of 9 years (range, 2-38 years), recurrence occurred in 169 patients with T3 tumors (16%), including 18 with pT3a (6%), 100 with pT3b (18%), 20 with pT3c (12%), and 31 with pT3d (48%). In a multivariate analysis, LN metastases (< 0.0001), extranodal extension (p = 0.03), FTC (vs. PTC) (p = 0.006), pT3b (p = 0.016), and pT3d (p = 0.047) were associated with an increased risk of recurrence. The 5-year RFS rates were 94.5, 82.2, 91.1, and 50.3% for the pT3a, pT3b, pT3c, and pT3d groups, respectively (p < 0.01).

Except for microcarcinoma, the risk of LN involvement is high and similar for the DTC patients with minimal ETE, regardless of the size of the tumor. The association of a tumor size of > 4 cm and ETE are associated with a poor prognosis and should justify the classification of these cases as a high-risk group. Other pT3 patients with no LN metastases could be individualized as a low-risk group.