New evidence for tumour embolism as a mode of metastasis

The demonstration that a significant proportion of patients with renal carcinomas of the clear cell type have tumour cell clumps or aggregates in venous outflow from the kidney has interest from two viewpoints. Firstly, the association of this occurrence with high VEGF-A production by the cancer seems to suggest a novel mode of 'budding' invasion where nests of tumour cells enter the dilated and mechanically fragile new vessels supplying the cancerous growth. Secondly, with the association of fragment occurrence and metastatic development, the entrance of clumps into the circulation indicates that epithelial-mesenchymal transition (EMT) is not an obligatory step for the disseminatory behaviour of all cancers.