Growth promotion and the tumour phenotype

As previously mentioned (section 3) levels of endogenous lipid peroxidation vary considerably in mammalian cells and a number of observations suggest an apparent inverse relationship between levels of lipid peroxidation and rates of cell proliferation and extent of cell differentiation. On the other hand the low level of lipid peroxidation reported for highly proliferating cells, whilst also observed in rapidly dividing tumour cells, does not appear to be specifically associated with the tumour phenotype. 

A particular feature however of a large number of tumour cell types is low levels of manganese-superoxide dismutase (Mn-SOD) activity [138]. Tumours are also usually low in copper, zinc-superoxide dismutase (Cu, Zn-SOD) activity and often also low in catalase activity [138]. Glutathione peroxidase levels are however quite variable. 

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