The extent of extrathyroidal extension is a key determinant of prognosis in T4a papillary thyroid cancer

Background and Objectives: In papillary thyroid cancer (PTC), the adverse prognostic impact of extrathyroidal extension (macro-ETE) invading the subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve (T4a disease) is well established. We investigated whether the extent of macro-ETE, defined as “limited” with single structure involvement (lim-ETE) and “extensive” with multiple structures involved (ext-ETE), influences prognosis in T4a PTC. Methods: A retrospective analysis of 610 patients with PTC identified 39 with T4a disease, including 26 with lim-ETE and 13 with ext-ETE. Univariate Cox regression was used to assess the relationship between the extent of macro-ETE and recurrence-free survival (RFS). Results: Ext-ETE was associated with a five times increased risk of recurrence compared to lim-ETE (HR 5.0, P <.030), with or without adjustment for radioactive iodine administration and after adjustment for margin status (HR 4.7; P =.041). A low-risk subset of T4a disease comprising of patients aged less than 55 years with lim-ETE and clear margins accounted for one-third of the cohort and demonstrated an excellent 5-year RFS of 92%. Conclusions: The extent of macro-ETE appears to be an important determinant of prognosis in T4a PTC. A low-risk subset of T4a disease exists with an excellent prognosis.