Abstract
Background: Angiogenesis has been found to be an important regulator in the disease progression of both solid tumors and hematologic malignancies. In solid tumors, the balance of pro and anti-angiogenic factors appears to be a critical factor in tumorigenesis, with disturbance in favor of angiogenesis promoting tumor growth and metastasis. This observation led to the concept of an “angiogenic switch” where pro-angiogenic influences outweigh anti-angiogenic factors. Patients with CLL have detectable levels of plasma and cellular pro and anti-angiogenic cytokines as well as abnormal neovascularization in the marrow and lymph nodes. Limited studies of pro-angiogenic cytokines have suggested that inter-patient variation in serum/plasma and cellular levels of these markers may have prognostic implications. We evaluated pro- and anti-angiogenic cytokines in a large sample of patients with CLL to evaluate the presence of angiogenic switching and its implications for disease progression.
Methods: In a prospective, longitudinal study, we analyzed the serum/plasma, intracellular(determined by flow cytometry), and CLL B cell secreted (24 hour medium values) levels of pro-angiogenic cytokines (VEGF, bFGF) and an anti-angiogenic cytokine (Thrombospondin [TSP]) in 311 patients with previously untreated CLL. VEGF:TSP and bFGF:TSP ratios were calculated to evaluate for evidence of angiogenic switching (higher ratio suggests a pro-angiogenic phenotype). The relationship of angiogenic cytokines to Rai stage, IgVH gene mutation status, % CD38 protein expression, and time to treatment (TTT) from the date of sample were evaluated (median follow-up=11 months). Sequential samples were available on >90% of patients and were evaluated to assess if changes in levels of angiogenic cytokines occurred in patients requiring treatment.
Results: Serum, cellular, and secreted levels of VEGF, bFGF, and TSP showed no correlation with Rai stage, IgVH gene mutation (continuous variable), or % expression of CD38 (continuous variable). However, among patients with Rai stage 0-II disease, individuals with lower TSP levels (<75 percentile, p=0.007) or higher bFGF:TSP ratios (continuous variable; p=0.003) had shorter TTT (Figure 1). Similar relationships for a shorter TTT were also observed for secreted TSP levels (p=0.007) and the cellular bFGF:TSP ratio (p=0.009). On analysis of sequential samples, no clear difference in serum, cellular, or secreted levels of VEGF, bFGF, TSP, VEGF:TSP, or bFGF:TSP occurred among those who required treatment.
Conclusions: Angiogenic cytokines appear to have prognostic significance in patients with previously untreated early stage CLL. Importantly, we report the original observation that the ratio of bFGF (pro-angiogenic) to TSP (anti-angiogenic) correlates with time to treatment as a continuous variable. This result provides further evidence that angiogenic switching relates to clinical progression in CLL. Longer follow-up of this cohort is needed to fully define the prognostic implications of angiogenic cytokines in CLL and determine if integration of these markers with other prognostic parameters improves risk stratification for early stage patients.
Survival According to Serum Thrombospondin Level
