title: Spindle cell and mixed spindle/lymphocytic thymomas: an integrated clinicopathologic and immunohistochemical study of 81 cases.
abstract: Forty-three cases of spindle cell thymoma (medullary, WHO type A) and 38 cases of mixed spindle/lymphocytic thymoma (WHO type AB) were studied for their clinicopathologic and immunohistochemical characteristics. Three histologic patterns of spindle cell thymoma were observed: short-spindled (57%), long-spindled (31%), and micronodular (12%). The short-spindled variant was composed of oval to short spindle cells commonly arranged in a hemangiopericytic or microcystic pattern. The long-spindled variant chiefly consisted of fibroblast-like epithelial cells mimicking fibrohistiocytic neoplasms. The micronodular variant was characterized by small nests of short spindle cells dispersed among a lymphoid stroma with frequent germinal centers. All kinds of spindle cell could be admixed with lymphocyte-rich "cortex"-like areas to constitute mixed spindle/lymphocytic thymomas. Immunohistochemically, the epithelial cells in up to 70% of the short-spindled and long-spindled variants of spindle cell thymoma and 90% of mixed spindle/lymphocytic thymomas were positive for CD20, whereas the epithelial cells in all micronodular spindle cell thymomas were negative. All of the spindle cell thymomas and most of the mixed spindle/lymphocytic thymomas in this study were found in stages I and II. Follow up of the patients did not disclose relapse or mortality directly resulting from the tumors. However, the prognosis of stage I and II spindle cell and mixed spindle/lymphocytic thymomas did not significantly differ from those of stage I and II thymomas of other types by a stage-matched survival analysis. Our data showed that spindle cell and mixed spindle/lymphocytic thymomas are distinctive in histologic pattern and immunohistochemical profile. When interpreted within the context of staging, spindle cell and mixed spindle/lymphocytic thymomas presenting in stages I and II most likely behave in an indolent fashion.
authors.affiliation: Department of Pathology, National Yang-Ming University and Veterans General Hospital-Taipei, Taiwan. ccpan@vghtpe.gov.tw
authors.forename: C C
authors.initials: CC
authors.lastname: Pan
authors.forename: W Y
authors.initials: WY
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Chiang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015703:Antigens, CD / Q000032:analysis; D000951:Antigens, Neoplasm / Q000032:analysis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008214:Lymphocytes / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000150:complications; D016019:Survival Analysis; D013945:Thymoma / Q000737:chemistry / Q000145:classification / Q000473:pathology*; D013953:Thymus Neoplasms / Q000737:chemistry / Q000145:classification / Q000473:pathology*
chemical_list: D015703:Antigens, CD; D000951:Antigens, Neoplasm