Neuroendocrine lung tumors: grade correlates with proliferation but not angiogenesis.

Angiogenesis has been implicated in the progression of human neoplasia from benign precursor to invasive and metastatic phenotypes. The acquisition of dominant oncogenes in preneoplastic cells in vitro and in vivo has been associated with the increased ability of tumor cells to secrete angiogenic mediators and recruit blood vessels. However, in a subset of benign lesions, high levels of angiogenesis have been found before the conversion to invasive and metastatic phenotypes. In many of these benign lesions, dominant oncogenic pathways are activated first; then as malignant potential is acquired, there is a loss of nuclear tumor suppressor genes, such as p53 and p16. We studied neuroendocrine lung tumors (NLT) ranging from typical and atypical carcinoid tumors to large cell neuroendocrine and small cell carcinomas in order to determine whether angiogenesis (as assessed by mean vessel density) and proliferation rates (as assessed by MIB-1 nuclear immunohistochemical staining) correlate with tumor type. We found that increased rates of proliferation, but not angiogenesis, correlate with tumor type. The association of increased proliferation and tumor type may prove to be clinically useful and shed light on the role of sequential oncogenic alterations in NLT.