Kit protein (CD117) and proliferation index (Ki-67) evaluation in well and poorly differentiated neuroendocrine tumors

Aims and background: Kit protein expression seems to be associated with a poor outcome in cancer patients and may be an important target for new anticancer drugs. We examined by immunohistochemistry the presence of Kit protein in neuroendocrine tumors (NETs) to explore its relationship with histological grade and proliferation index. Patients and methods: Thirty-five tumor specimens from patients with 24 well differentiated and 11 poorly differentiated NETs were examined for the presence of Kit protein and the proliferation index marker Ki-67. Results: Eleven specimens were positive for Kit protein expression, 8 of which had poorly-differentiated histology and only 3 had well-differentiated histology. Most of the tumors showing immunopositivity for Kit protein were also characterized by a high proliferation index. Conclusions: Immunohistochemical positivity for Kit protein is mainly related to poorly differentiated NETs. In our study, the percentage of tumors with immunopositivity for Kit protein was lower than that observed by other authors. This difference could be attributable to the different immunohistochemistry procedures used and to the biological heterogeneity of NETs. The number of Kit protein-positive NETs may justify targeted therapy with a tyrosine kinase receptor-associated inhibitor only in a selected subset of patients, whenever no other therapy is available and an autocrine loop sustained by the Kit receptor and its specific ligand has been demonstrated.