Okada et al reported that atypia was frequently observed in tumors with higher cellularity, which was independent of the tumor size and histological appearance.10 In addition, proteins related to malignancy and proliferative activity, such as p53, ki-67 and PCNA, are more frequently observed in tumors with higher cellularity, and of these, p53 is thought to be a prognostic factor.11, 12 The most frequently reported sites of metastases of pleural SFTs are the lungs and the pleura; other sites include the brain and the liver. The gene discussed is MKI67; the disease is neoplasm.