Cancer is primarily a disease of ageing epithelia, and of ageing indiv
iduals. We now possess detailed insights into the changes in cell regu
latory genes and DNA repair systems which accumulate with time and whi
ch manifest in malignancy. These demonstrate how cancer is frequently
characterized by degenerative change in the genotype, from the most su
btle base pair mutations to gross aneuploidy, and by deterioration in
cell and tissue regulatory control, be it of proliferation, programmed
cell death or signalling. Cancer may thus be as much a phenomenon of
loss or deterioration of normal genomic control as of the acquisition
of new, neoplastic functions. This distinction may be more than semant
ic, not least because it governs our approach to the search for therap
eutic strategies. This essay considers the concept of cancer as a dege
nerative disease and its implications, and proposes the neologism aldo
plasia to describe this phenomenon of cancer biology.