## 1 Introduction  
Angiogenesis is a biological process that leads to the formation of new capillaries from existing blood vessels. It is an integral part of physiological processes, such as embryonic development, wound healing, and ovulation. It is also present in disease and pathological conditions, which include, among others, cancer, arthritis, and diabetic retinopathy. Angiogenesis is significantly enhanced in cancer metastasis, which is the most severe stage of disease. It is regulated by various growth factors, including vascular endothelial growth factor (VEGF-A) and fibroblast growth factor-2 (FGF-2) [1]. VEGF-A is the main mediator of vascular hyperpermeability, as well as angiogenesis and inflammatory processes involved in tissue repair. A single human VEGF-A gene accounts for at least eight isoforms (VEGF-121, VEGF-145, VEGF-148, VEGF-165, VEGF-183, VEGF-189, and VEGF-206), which vary in quantity in tissues [2]. The concentration of VEGF-A in the serum of healthy human subjects has been reported as equal to 550 pg/mL [3], 155-310 pg/mL [4], 48-106 pg/mL [5], or 160 \(\pm\) 126 pg/mL [6]. VEGF-A concentration in human plasma is significantly lower (32 \(\pm\) 22 pg/mL) [6]. Considering the data from the studied groups in the cited articles, we believe that the concentration of VEGF-A in healthy donors should range from about 34 pg/mL to about 310 pg/mL. VEGF-A(165) is widely regarded as a potent vascular permeability enhancer that is dominant in physiological and pathological angiogenesis. It has the ability to interact with many VEGF receptors; therefore, this isoform is primarily involved in the induction of proliferation, migration, and cell survival. As a result, VEGF-A(165) is regarded as a protein that is probably able to regulate all stages of both physiological and pathological angiogenesis [7]. In haematological tumours, VEGF-A is responsible for the growth, survival, and migration of cells. Moreover, it positively influences the self-renewal of leukemic progenitor cells. A study found that the concentration of VEGF-A increased, in some cases by almost seven times, in children with ALL compared with the control group [8]. FGF-2 (bFGF) is one of 23 members of the group of fibroblast growth factors. Two isoforms of 18 and 24 kDa are mainly involved in biological processes. FGF-2 forms with masses of 22, 22.5, and 34 kDa have also been isolated. FGF-2 proteins are responsible for the most important biological functions, such as acquisition of the survival phenotype and regulation of gene expression [9]. FGF-2 also has alternative isoforms that result from appropriate mRNA translations. These include the cytoplasmic isoform with a mass of 17 kDa and two others with higher molecular weights of 21 and 23 kDa [10]. The concentration of FGF-2 in human serum is rarely reported, and no clear data concerning FGF-2 levels are available. Values of 275 \(\pm\) 235 pg/mL [11] and 1.54 \(\pm\) 1.98 pg/mL [6] are reported for healthy subjects; while taking into account the clinical description, we are more inclined to accept the value of 1.54 \(\pm\) 1.98 pg/mL. For this reason, new and more reliable methods for its determination are desirable. Little is known about the role of FGF-2 (17 kDa) in leukaemia. However, it is known that this isoform is responsible for the proliferation of cells (astrocytes) which are crucial in cases of [PERSON]'s disease. The promotion of the proliferation of these cells has a positive influence in the form of a protective effect of FGF-2 (17 kDa) in Alzheimer's disease [10]. On the other hand, rat prostate cancer cells were found to contain significant levels of FGF-2 (17 kDa), indicating that this isoform is associated with neoplastic transformation [12]. The fundamental role of angiogenesis is confirmed, first of all, in the growth and metastasis of solid tumours [13]. However, there are reports that suggest that angiogenesis may also play a role in the pathogenesis of haematological neoplasms.