Fig. 6.

The journey of a metastatic cell: from the primary site to the secondary site. Cancer cells have a “long and difficult” journey to go on before colonizing a secondary site and form metastases. This journey comprises several milestones that are summarized as follows: a Proliferation of primary tumour, b Local invasion of detached cells. c Intravasation in a capillary, and tumour cell survival in blood circulation: 1, interaction with leukocytes that may be destructive or not; 2, aggregation with platelets, which protects cancer cells against mechanical stress and leukocytes; 3, tumour cell–cell aggregation, which protects against stress and formation of intra capillary thrombosis. d Arrest and extravasation in a target organ. e Metastatic growth in the new appropriate environment and formation of a secondary neoplasm