We appreciate the comments and suggestions by the reader. Available literature shows that there is a controversy regarding the best blood compartment and the best test to measure VEGF in cancer patients. VEGF in cancer patients is the sum total of platelet derived VEGF as well as other sources like neo-angiogenesis in the tumor tissue. One of the studies showed that the best discrimination between healthy volunteers and cancer patients was observed in platelet poor plasma (PPP). As gene-rating plasma induces platelet activation with consequent VEGF release from platelets, citrate-theophylline-adenosine-dipyridamole plasma was suggested by some authors to evaluate VEGF [1]. Serum VEGF is more practical because VEGF levels in citrated plasma are low and lie close to the limits of ELISA sensitivity. Some studies have shown that a standardized measurement of serum VEGF, normalized by the patient’s platelet count, which gives a value of serum VEGF per platelet, can be a useful parameter [2].

We had our baseline platelet counts for all the patients but the corresponding platelet counts for subsequent follow up (A2 and A3) assessments were not available for all patients [3]. Hence, we restricted our analysis to baseline values only. On applying pair wise correlation to the baseline platelet count and serum VEGF, we found an insignificant correlation; r=0.16 (P=0.09) (Fig. 1a). Baseline serum VEGF showed a significant positive correlation with baseline VEGF per platelet (r=0.81, P<0.0001) (Fig. 1b). As the serum VEGF and VEGF/per platelet correlate significantly, both are likely to follow similar trends; this implies that we are likely to have similar observations, whether we use serum VEGF or VEGF/platelet.

Fig. 1 Scatter plots showing correlation between (a) baseline VEGF and baseline platelet counts, and (b) baseline VEGF and baseline VEGF per platelet.

Similar observations were reported by Vermeulen, et al. [4]; they commented that in view of the lack of a strong association between serum VEGF and platelet count, and the association of serum VEGF with the degree of stimulation of endothelial cell proliferation in vitro, measuring serum VEGF might be more suitable in cancer patients than measuring plasma VEGF. Also, it has been postulated that at least part of the VEGF in platelets represents that endocytosed from the plasma due to their scavenging effect [4]. So, measuring the entire collection (serum VEGF) may not be less appropriate.

Further, most previous studies on metronomic chemo-therapy had measured serum VEGF and we intended to be consistent and comparable to them [5,6]. Hence, our conclusion remains the same that VEGF is not a reliable biomarker for metronomic chemotherapy, but the best test for VEGF still remains an illusion.

1. Wynendaele W, Derua R, Hoylaerts MF, et al. Vascular endothelial growth factor measured in platelet poor plasma allows optimal separation between cancer patients and volunteers: A key to study an angiogenic marker in vivo? Ann Oncol. 1999;10:965-71.

2. George ML, Eccles SA, Tutton MG, Abulafi AM, Swift RI. Correlation of plasma and serum vascular endothelial growth factor levels with platelet count in colorectal cancer: Clinical evidence of platelet scavenging? Clin Cancer Res. 2000;6:3147-152.

3. Pramanik R, Tyagi A, Agarwala S, Vishnubhatla S, Dhawan D, Bakhshi S. Evaluation of vascular endothelial growth factor (VEGF) and thrombospondin-1 as bio-markers of metronomic chemotherapy in progressive pediatric solid malignancies. Indian Pediatr. 2020; 57:508-11.

4. Vermeulen PB, Salven P, Benoy I, Gasparini G, Dirix LY. Blood platelets and serum VEGF in cancer patients. Br J Cancer. 1999;79:370-73.

5. Kesari S, Schiff D, Doherty L, et al. Phase II study of metronomic chemotherapy for recurrent malignant gliomas in adults. Neuro Oncol. 2007;9:354-63.

6. Kieran MW, Turner CD, Rubin JB,　et al. A feasibility trial of antiangiogenic (metronomic) chemotherapy in pediatric patients with recurrent or progressive cancer. J Pediatr Hematol Oncol. 2005;27;573-81.