Extrathyroidal extension in well-differentiated thyroid cancer: macroscopic vs microscopic as a predictor of outcome

Objective: To examine the prognostic difference in well-differentiated thyroid cancer between macroscopic extrathyroidal extension (ETE), which is appreciated in the operating room, vs microscopic ETE, which is only appreciated under the microscope by the pathologist. Design: Retrospective medical record review. Setting: Tertiary care academic hospital. Patients: Among 582 patients, those who were surgically treated for stage III well-differentiated thyroid cancer with a minimum 5-year follow-up were included. Fiftyfive patients (10%) (17 males and 38 females [mean age, 53.1 years]) met the selection criteria. Main Outcome Measures: Disease-specific survival and overall survival. Results: Thirty-two patients (58%) had macroscopic ETE, while 23 patients (42%) had microscopic ETE. Twenty-year disease-specific survival in the macroscopic group was 47% (8 of 17) and 45% (5 of 11) in the microscopic group (P=.45). Twenty-year overall survival in the macroscopic group was 27% (3 of 11) and 24% (4 of 17) in the microscopic group (P=.59). The only confounding factor was external beam radiation therapy (EBRT). More patients with macroscopic ETE were treated with EBRT (P=.007). When survival was stratified according to EBRT, patients with macroscopic ETE who did not receive EBRT had diminished disease-specific survival (P=.07) and overall survival (P=.12). On multivariate analysis, EBRT was the only predictor of improved disease-specific survival (P=.02) and overall survival (P=.06). Conclusions: In selected patients with macroscopic ETE, we recommend postoperative EBRT. Further investigation is required to determine whether macroscopic ETE vs microscopic ETE is an independent predictor of outcome.