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

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.