Expression of tyrosine kinase receptors in malignant midgut carcinoid tumors

Background: The expression of certain tyrosine kinase receptors (TKR) has been shown to have a prognostic value in many tumor entities. In recent years, inhibitors and monoclonal antibodies directed towards these receptors have been developed. Several have shown antitumoral effects and have been tested in clinical trials. We wanted to investigate whether midgut carcinoid tumors express TKR and therefore would be suitable for clinical trials with TKR inhibitors (TKRI) or monoclonal antibodies. Material and Methods: Tumor tissue from 36 patients (24 women and 12 men) with a malignant midgut carcinoid tumor was obtained. The tissues were examined with immunohistochemistry, using polyclonal antibodies against platelet-derived growth factor receptor-alpha (PDGFR alpha), platelet-derived growth factor receptor-beta (PDGFR beta), epidermal growth factor receptor (EGFR) and c-kit. Human BON1 cells were cultivated and stimulated with PDGF-BB. We also present a case report of a patient with a malignant midgut carcinoid tumor who had stabilization of tumor growth during treatment with imatinib. Results: Immunohistochemical staining for PDGFR alpha in tumor cells showed immunoreaction for the receptor in 13/34 (38%) for PDGFR beta in 29/33 (88%), and 24/33 (73%) were immunoreactive for EGFR. No tumor tissue showed immunoreaction for c-kit. In tumor stroma PDGFR alpha was expressed in 35%, PDGFR beta in 94% and EGFR in 9%. We show that human neuroendocrine tumor cells respond to PDGF, indicating that these tumors express functional PDGF receptors. Conclusion: Malignant midgut carcinoid tumors may express three of the four TKR tested in this investigation. Therefore, these tumors might be susceptible for treatment with TKRI or monoclonal antibodies and this should be further explored in clinical trials. Copyright (c) 2006 S. Karger AG, Basel.