Until now little information is available about bone marrow (BM) angiogenesis in chronic
myeloproliferative disorders (CMPDs). Amongst the various immunohistochemical markers for endothelial cells CD34 and CD105 have proven to be most reliable since they exhibit no relevant co-staining. Determination of vascularity has to include pathophysiological aspects of perfusion. Therefore, quantification of the microvascular density (MVD) by the so-called hot spot method has to be improved by parameters that characterize blood flow more properly like microvessel area (
luminal distension), shape (form factor), tortuosity, and branching (maximal vessel length). In comparison to the normal BM
chronic myeloid leukemia (CML) revealed a significant increase in MVD which was functionally associated with elevated levels of angiogenic
cytokines. Structure of vessels was significantly altered by showing an enhanced irregularity of shape and tortuosity and increase in fibers was conspicuously accompanied by a higher degree of MVD. Contrasting the group of patients with
Imatinib (
STI571)
therapy interferon failed to reduce the number of vessels. Following
bone marrow transplantation a significant enhancement of the MVD was found in the early post-transplant period, but after about 6 months normalization occurred. Anomalies of microvascular architecture were easily demonstrable by three-dimensional reconstruction and consisted of a complex branching network of irregular shaped sinuses.
Chronic idiopathic myelofibrosis displayed a significant increase in the MVD only in the advanced fibrosclerotic stages. This feature was accompanied by an enhanced
luminal distension and tortuosity, thus contrasting the prefibrotic and early fibrotic phases of this disorder. Similar to CML a relationship between evolving
myelofibrosis and change in vascular architecture was encountered. This feature may present a possible target for future anti-angiogenic
therapy. In
essential thrombocythemia there is only a mild increase in MVD detectable while in
polycythemia vera besides an enlarged number, a
luminal dilation due to the densely packed erythrocytes is recognizable. In conclusion, contrasting the usually applied quantification technique more elaborate morphometrical methods are warranted to obtain a better insight into the vascular architecture of the BM. In CMPDs angiogenesis is significantly associated with the evolution of
myelofibrosis and may be altered by therapeutic regimens probably due to changes in
cytokine release.