Metastatic risk profile of microscopic lymphatic and venous invasion in papillary thyroid cancer.

[OBJECTIVES] The aim of this study was to define the suitability of microscopic lymphatic and venous invasion for prediction of lymph node and distant metastases in papillary thyroid cancer.

[DESIGN] Stratification by microscopic lymphatic and venous invasion, and multivariable analyses on lymph node and distant metastases including microscopic lymphatic and venous invasion as independent variables.

[SETTING] Tertiary referral centre.

[PARTICIPANTS] 422 patients who had ≥5 lymph nodes removed at initial thyroidectomy.

[MAIN OUTCOME MEASURES] Lymph node and distant metastases.

[RESULTS] Patients with microscopic lymphatic invasion had larger primary tumours than patients without and more often revealed microscopic venous invasion, multifocal tumour growth and lymph node metastases. Patients with microscopic venous invasion exhibited larger primary tumours than patients without and more commonly had microscopic lymphatic invasion, poor tumour differentiation, lymph node metastases and distant metastases. Prediction of lymph node metastases by microscopic lymphatic invasion was better than prediction of distant metastases by microscopic venous invasion regarding sensitivity (61.0 vs. 33.3%) and positive predictive value (92.6 vs. 20.9%), comparable regarding specificity (89.6 and 93.4%), and worse regarding negative predictive value (51.9 vs. 95.3%) and accuracy (70.1 vs. 87.7%). On multivariable logistic regression analysis, microscopic lymphatic invasion was associated with lymph node metastasis (odds ratio [OR] 11.1) and multifocal tumour growth (OR 2.4), whereas primary tumour size (OR 5.8 for tumours >40 mm relative to tumours ≤20 mm) and multifocal tumour growth (OR 3.1) were associated with distant metastasis.

[CONCLUSION] Stricter histopathological criteria are warranted to enhance the utility of microscopic vascular invasion for prediction of distant metastases in papillary thyroid cancer.