Importance of Number of Foci of Capsular Invasion in Follicular Thyroid Carcinoma.

The importance of capsular invasion in follicular thyroid carcinoma (FTC) has not been extensively studied. The aim of the present study was to correlate the clinical features and outcome of FTC with histology features particularly emphasizing on the importance of the number of foci of capsular invasion. This was a retrospective study. Histology of 123 FTC patients was reviewed. Patients were divided in three groups based on the number of foci of vascular and capsular invasion noted in primary tumor: group 1-capsular invasion at <6 and vascular invasion at <4 foci, group 2-either capsular invasion ≥6 or vascular invasion at ≥4 foci, and group 3-capsular invasion ≥6 and vascular invasion at ≥4 foci. Different prognostic factors and overall survival (OS) were compared among the groups. The incidences of distant metastases ( p  = 0.008) and OS ( p  = <0.001) were significantly different among the groups. On univariate analysis, age ( p  = 0.001), tumor size ( p  = <0.0001), distant metastases ( p  = <0.0001), vascular invasion ( p  = 0.018), and capsular invasion ( p  = 0.003) were significantly associated with OS. On multivariate analysis, age ( p  = 0.020), distant metastases ( p  = 0.045), and foci of capsular invasion ( p  = 0.005) were significant. The number of foci of capsular invasion seems to have significant prognostic value in widely invasive FTC.