MUC1 and Cowden syndrome 1: At a cutoff of 300 U/mL, KL-6 distinguished CS from SS with an area under the curve (AUC) of 0.756 (sensitivity, 75.3%; specificity, 69.7%) and performed better in distinguishing CS from DEWs (AUC = 0.842; sensitivity, 74%; specificity, 84%).