It is with great interest that I have read the article by Fukui et al. [1]. Spontaneous regression of thymic epithelial tumours is rare according to the international bibliography and the three cases presented are really interesting. The regression of thymic epithelial tumours is not well explained but it looks that there is an important role of autoantibodies in such incidents, and in other autoimmune disorders related with thymomas [2]. There are cases reported in the literature related to thymic hyperplasia due to systemic chemotherapy and complete remission after finishing it. The thymus gland seems to be a part of the immunological mechanism not well understood until now [3]. The treatment for thymomas is surgical and, according to the type, radiotherapy or chemotherapy can follow [4]. In selective patients in whom absence of malignancy is proven by computed tomography (CT)-guided biopsy or else, repeated CT scanning can reveal such cases of spontaneous regression of thymic tumours, and lead to radiological and clinical monitoring rather than surgical treatment. High index of suspicion and supervision is mandatory in such cases [5]. Conflict of interest: none declared