Background: VEGF is the key factor in angiogenesis which is essential for the development and progression of solid tumours. VEGF acts via two high affinity receptors: KDR and FLT-1. FLT-1 exists both in membrane-fixed and soluble forms. The soluble form is perhaps the only known natural direct antagonist of VEGF and may have a role in anti-angiogenesis therapy.
Materials and methods: We developed an in-house ELISA and have assayed soluble FLT-1 in the sera of cancer patients. We assayed preoperative serum from 50 colorectal and 43 breast cancer patients, and paired serum and plasma from 20 healthy volunteers. Postoperative serum from 17 colorectal cancer patients was also assayed.
Results: No s FLT-1 was detected in the samples from the healthy volunteers. Soluble FLT-1 was detected in the serum of both colorectal and breast cancer patients. We did not find any correlation between s FLT-1 and stage of either cancers. There was no significant correlation between serum VEGF and s FLT-1. Serum FLT-1 was markedly decreased in the postoperative serum of patients with detectable preoperative levels and none of the receptor negative sera became positive postoperatively.
Conclusion: We conclude that s FLT-1, a natural antagonist of VEGF, is detectable in the sera of cancer patients. Larger studies involving long term follow-up are required to determine its prognostic significance.