We received fresh tissue from a mediastinal mass (female aged 57), teased
it into a suspension and typed it by flow. >90% of cells showed a
phenotyoe of TdT+ CD1a+ CD2+CC3+ CD4+ CD8+ CD5+ CD7+ with 50% CD10+. This
would be consistent with T cell lymphoblastic lymphoma with a cortical
thymocyte phenotype. The majority of cells in the cytospin showed the
morphology of lymphoblasts.It was noted that the Ki-67 was <1% - unusual
for TLL.
Immunophenotyping performed on parrafin embedded sections revealed the
presence of a population of cells which were Cytokeratin positive and a
diagnosis was made of cortical thymoma. The T "blasts" we typed were
therefore a background population.
Cytokeratin staining on our cytospins showed occasional poorly preserved
cells positive. Presumably most of the thymoma cells didn't survive the
processing.
The question is , what is the significance of CD10 positivity on cortical
thymocytes. Is it a normal finding on CD4+CD8+ cells in human thymus?
We see it often in T cell ALL and T lymphoblastic lymphoma and initially
assumed in this setting that it was suggestive of a maligancy prior to the
review of the histology.
Thanks
Jan
Jan Nelson
Molecular Haematology
Department of Molecular Medicine
The University of Auckland
Phone: (+64)(9) 373-7599 ext 6381
Fax: (+64)(9) 373-7292