VEGFR1-activity-independent metastasis formation.

Molecules such as vascular endothelial growth factor (VEGF) or placental growth factor-critical regulators of tumour angiogenesis-are also thought to mobilize into blood circulation bone marrow-derived cells (BMDCs), which may subsequently be recruited to tumours and facilitate tumour growth and metastasis. A study has suggested that BMDCs form 'metastatic niches' in lungs before arrival of cancer cells, and showed that pharmacological inhibition of VEGF receptor 1 (VEGFR1, also known as Flt1)-cognate receptor for VEGF and placental growth factor-prevented BMDC infiltration in lungs and 'metastatic niche' formation. Here we report that blockade of VEGFR1 activity does not affect the rate of spontaneous metastasis formation in a clinically relevant and widely used preclinical model. Therefore, alternative pathways probably mediate the priming of tissues for metastasis.