Angiogenesis is an essential process in the progression of malignant tumours. A variety of proteins, including growth factors and extracellular matrix enzymes, have been recognised to be potent inducers of angiogenesis. 26
Recent evidence suggests that tumour angiogenesis is associated with patient outcome in several malignancies. Therefore, neoangiogenesis may become an integral part of a more consistent staging system. The first study correlating MVD with prognosis in NSCLC was that of Macchiarini and colleagues 4
in 1992, who assessed neovascularisation by the use of anti-factor VIII. Later, factor VIII, 6,
and VEGF expression, 5,
in addition to non-vascular growth factors 30
were investigated. Comparisons and meta-analysis are very difficult to perform because of the different methodologies and evaluation criteria for VEGF and MVD used, in addition to the heterogeneity of the study samples (table 8).
Studies correlating neoangiogenesis and survival in NSCLC
Such different results highlight the need for more reliable markers of neoangiogenesis. Nevertheless, recently Meert and colleagues 26
performed a meta-analysis based on a systematic review of the literature to assess the prognostic value on survival of microvessel count in patients with lung cancer. They found that a high MVD was a significantly poor prognostic factor for survival in NSCLC, however it was assessed (factor VIII, CD34, or CD31).
The purpose of our study was to identify the best markers of neoangiogenesis and correlate them to survival in a group of patients with early stage NSCLC. To the best of our knowledge, this is the first study dealing with such a wide panel of factors in such a selected group of patients.
Our data show that patients classified at the same prognostic stage according to classic morphological criteria have very variable prognoses. Within this group, we found that some markers of neoangiogenesis were useful tools to characterise patients with a poor outcome.
“Interestingly, CD105 proved to be a significant marker of neoangiogenesis, but it was excluded at multivariate analysis”
Our results show that high VEGF expression, high MVD as assessed by CD105 and CD34, and tumour vessel invasion are good markers of angiogenesis and are significantly correlated with a poor survival rate. Nevertheless, at multivariate analysis, only MVD assessed by CD34 and tumour vessel invasion were selected by the statistical model. The combination of these two markers classified three populations with different risks of dying.
Interestingly, CD105 proved to be a significant marker of neoangiogenesis, but it was excluded at multivariate analysis. This finding contrasts with the results of Tanaka et al
who found that CD105 expression was the best marker of angiogenesis and was a significant prognosticator of disease free survival, superior to CD34. This apparent contradiction might be explained by the fact that CD34 and tumour vessel invasion are more strictly related to the metastatic process than neoangiogenesis by itself. Yano et al
have recently demonstrated a higher incidence of distant metastases and a shorter survival in patients with high grade MVD as assessed by CD34. 5
A significant correlation was also shown between CD34 and tumour vessel invasion.
Take home messages
- Patients with non-small cell lung cancer with vascular endothelial growth factor (VEGF) overexpression, high microvessel density (MVD) by CD34 and CD105, and tumour vessel invasion had shorter overall survival on univariate analysis
- Multivariate analysis showed that MVD by CD34, tumour vessel invasion, and VEGF expression were significant predictive factors for overall survival
- The presence of both tumour vessel invasion and MVD by CD34 was highly predictive of poor outcome and might be useful to identify a subset of high risk patients who could be targeted for more aggressive treatment
The limitations of our study are the small sample size and the length of the minimum follow up required. As far as the size of the study group is concerned, we chose only a particular subset of patients (stages IB–IIA) to avoid bias resulting from different prognoses. Indeed, even if these patients are staged into different classes the prognosis is similar. 17,
Conversely, stage I, compounded with IA and IB, is a heterogeneous group. Nevertheless, despite the relatively short follow up period, we were able to demonstrate a significant impact of the expression of the analysed factors on survival.