Immunohistochemical Expression of Vascular Endothelial Growth Factor Correlates with Microvessel Density in Ph⁻ Chronic Myeloproliferative Disorders.

There is increasing evidence that neovascularization may play an important role in hematological malignancies (particularly lymphomas, acute leukemia and myelodysplastic syndromes), but only a few studies have been performed in Ph⁻ chronic myeloproliferative disorders (CMPDs). Increased angiogenesis has been reported in chronic idiopathic myelofibrosis (CIMF), whereas high serum levels of vascular endothelial growth factor (VEGF) have been described in Ph⁻ CMPDs. These findings have led to the use of new therapeutic approaches aimed at directly targeting endothelial cells or VEGF. The aim of this study was to evaluate microvessel density (MVD) and immunohistochemical VEGF expression in the different categories of Ph⁻ CMPD. We examined the bone marrow biopsies (BMBs) of 98 Ph⁻ CMPD patients, classified as follows on the basis of the WHO criteria: 29 cases of essential thrombocythaemia (ET), 39 cases of CIMF (11 CIMF-0, 11 CIMF-1, 7 CIMF-2 and 10 CIMF-3) and 30 cases of polycythemia vera (PV) (20 polycythemic phase [pp-PV] and 10 post-polycythemic myelofibrosis [post-PVMF]. We also analysed 20 normal BMBs of subjects not suffering from hematological disease. MVD was analysed using the “hot-spot” method and an anti-CD34 antibody. Immunohistochemical VEGF expression was expressed as a VEGF index based on the formula [VEGF(i) = VEGF(+) cells x BMB cellularity/100]. Data were statistically tested at the 5% significance level (p<0.05; one-way ANOVA; Tukey’s HSD test; Pearson test). MVD was significantly greater in the CIMF and PV patients (respectively 25.6 ± 6.3 and 20.7 ± 10.2) than in the ET patients (10.1 ± 4.5) or controls (7.5 ± 3.6) (p<0,01). No differences were found in relation to the CMF grading score (CIMF-0: 24.7 ± 6.5; CIMF-1: 26.1 ± 6.4; CIMF-2: 25.3 ± 4.9; CIMF-3: 26.2 ± 7.5), but post- PVMF patients had higher microvessel counts than the pp-PV patients (31.9 ± 7.3 vs 15.1 ± 5.9; p<0.01). There were also significant differences in VEGF(i) between the CIMF and PV patients (respectively 0.29 ± 0.15 and 0.28 ± 0.20) and the ET patients (0.12 ± 0.05) or controls (0.08 ± 0.04). There were no significant differences among the different grades of fibrosis (CIMF-0: 0.25 ± 0.15; CIMF-1: 0.32 ± 0.17; CIMF-2: 0.36 ± 0.16: CIMF-3: 0.27 ± 0.14), but a remarkable difference was found between the pp-PV and post-PVMF patients (0.21 ± 0.15 vs 0.49 ± 0.19; p<0.01). Finally, there was a strong correlation between MVD and VEGF(i) in the patients with CIMF (0.4006; p=0.013) and those with PV (0.7923; p<0.01). In conclusion, our findings show that angiogenesis was not different in ET patients and normal controls, whereas both MVD and VEGF levels were significantly higher in the patients with CIMF or PV, and showed a correlation between them. If confirmed, these results could serve as a rational guide for the anti-angiogenetic therapy of Ph⁻ CMPD.