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. Fifty-five 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.