Author(s): Ferguson M
Angiogenesis, the growth of new blood vessels, is vital to tumour growth. Prevailing dogma has been that tumours cannot grow without angiogenesis. Based on this premise, anti-angiogenic drugs are used clinically. However, the principle of angiogenesis as an absolute requirement for tumour growth has been challenged with reports that many tumours are entirely or partially non-angiogenic. This study describes and quantifies characteristics of non-angiogenic non-small cell lung tumours, demonstrates non-angiogenic growth in small-cell/neuroendocrine lung tumours and investigates the underlying pathogenetic processes by comparison with angiogenic lung tumours. Hypoxia is an important stimulus for angiogenesis. Differences in response to hypoxia may determine whether a tumour produces new vessels. In order to test this, levels of. necrosis, often considered a surrogate marker of hypoxic stress, were quantified but no difference in quantity of necrosis was found Moreover, immunohistochemical investigation of hypoxia and angiogenesis factors provided no unambiguous explanation for the differences in angiogenesis. Significant differences were seen, however, in fibrosis and inflammation, which were both greater in angiogenic tumours. Differences were greater for lymphocytes rather than cells of the ‘innate’ immune system. This provided an alternative hypothesis: angiogenesis occurs during wound healing and in the growth of granulation tissue, so it is possible that tumour angiogenesis is a response to factors produced by immune cells rather than the tumour itself. A tumour’s angiogenic status may, therefore, be determined by the response it provokes from the immune system. Further work to test this theory would compare levels of immunogenic factors such as Tumour Necrosis Factor and tumour cell surface antigens such as the HLA class I molecules. The study concludes with an investigation into the molecular basis of non-angiogenic growth using the technique of comparative genomic hybridisation (CGH) which allows amplifications and deletions of areas of DNA to be calculated. High-resolution array CGH was evaluated against conventional CGH, and the results compared with previous RNA studies from our laboratory. These revealed a set of genes with consistent changes in both RNA and DNA, several of which form part of known angiogenic and inflammatory pathways.