Rare expression of KIT (CD117) in lymphomas: a tissue microarray study of 1166 cases

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Abstract
Aims : Imatinib mesylate specifically inhibits KIT tyrosine kinase activity, and has been proven to be effective in the treatment of gastrointestinal stromal tumours. Because other KIT‐expressing malignancies might benefit from Imatinib therapy, we evaluated the distribution and expression of KIT in 1166 cases of malignant lymphoma. Materials and results : Tissue microarrays (TMAs) containing 824 non‐Hodgkin's lymphoma (NHL) and 342 Hodgkin's lymphoma (HL) cases were immunohistochemically analysed for the expression of the KIT protein. Two KIT‐positive NHLs were sequenced using polymerase chain reaction analysis. One T‐cell lymphoma and one follicular lymphoma of the 747 NHL cases (0.3%) were positive for KIT. All HLs were Kit‐negative. None of the KIT‐positive cases showed a kit gene mutation. Conclusions : KIT expression is a very rare event in NHL and virtually absent in HL. In the few positive cases, the aberrant expression is not caused by a mutation in the ‘hot‐spots’ of the kit gene, indicating that treatment of these tumours with Imatinib may be ineffective.