Lymphovascular invasion and risk of recurrence in papillary thyroid carcinoma

Background: Lymphovascular invasion (LVI) is an established adverse prognostic factor in many cancers, however, there are few studies assessing its significance in papillary thyroid carcinoma (PTC). We aimed to determine if LVI is an independent prognostic factor in PTC. Methods: We conducted a single institution retrospective analysis of 610 patients with PTC treated between 1987 and 2016. LVI was defined as the presence or absence of cancer cells in blood vessels and/or lymphatics on histopathology. Multivariate Cox regression analysis was used to evaluate the association between LVI and recurrence-free survival (RFS). Results: The study cohort included 481 (78.9%) females and 129 (21.1%) males, with a median age of 47.6 years and median follow-up of 3.4 years. LVI was present in 56 (9.2%) patients and was associated with nodal metastases (P < 0.001), extrathyroidal extension (P < 0.001), extranodal extension (P < 0.001), multifocality (P = 0.018) and microscopic positive margins (P < 0.001). On univariate analysis, LVI was associated with reduced RFS (hazard ratio (HR) 2.3; 95% confidence interval (CI) 1.3–4.3; P = 0.007). However, after adjusting for nodal stage (pN0, pN1a, pN1b) there was no association between LVI and RFS (HR 1.3; 95% CI 0.7–2.5; P = 0.398). Similar results were obtained in full multivariate models adjusting for additional prognostic factors (HR 1.2; 95% CI 0.6–2.4; P = 0.627). Conclusion: LVI is strongly associated with other adverse prognostic factors in PTC, particularly the presence and extent of nodal metastases. However, after adjusting for these, LVI is not an independent predictor of recurrence.