Non-haematological solid tumours as surrogate granulocytes: a possible mechanism for metastatic spread

The concept that non-haematological solid tumours utilize normal leukocyte mechanisms, specifically those of granulocytes, to facilitate metastatic spread is presented here. In this article we will address the question of whether the process of metastasis is a phenomenon unique to tumour cells that utilize unique processes that are only found in neoplastic cell populations, or whether neoplastic populations ‘turn on’ or co-opt latent leukocyte genes normally not expressed by the parental, normal tissue of origin. We suggest that ectopic expression of leukocyte genes in epithelial tumours may be the simplest method for solid tumours to acquire the mechanisms for neoplastic spread through metastasis and may also account for the observed lack of host immunosurveillance of such tumours.