Spindle cell and mixed spindle/lymphocytic thymomas: an integrated clinicopathologic and immunohistochemical study of 81 cases

Am J Surg Pathol. 2001 Jan;25(1):111-20. doi: 10.1097/00000478-200101000-00013.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antigens, CD / analysis
  • Antigens, Neoplasm / analysis
  • Female
  • Humans
  • Immunohistochemistry
  • Lymphocytes / pathology
  • Male
  • Middle Aged
  • Myasthenia Gravis / complications
  • Survival Analysis
  • Thymoma / chemistry
  • Thymoma / classification
  • Thymoma / pathology*
  • Thymus Neoplasms / chemistry
  • Thymus Neoplasms / classification
  • Thymus Neoplasms / pathology*


  • Antigens, CD
  • Antigens, Neoplasm