[Telomere].
We reviewed correlations among telomere length, aging and carcinogenesis. Southern blot analysis showed that telomere shortening occurred with aging in all human tissues except for brain and myocardium. We investigated the telomere lengths of individual cell types in human tissues using a Q-FISH method and an original software package, "Tissue Telo". Q-FISH revealed that in squamous epithelia, NTCR corresponding to telomere length was significantly highest in basal cells and lowest in prickle cells, and that telomere length regressed at a certain rate in each cell type except for fibroblasts. Mean telomere length was significantly less in background tissue squamous epithelia of patients with cancer than in normal controls without cancer. We demonstrated telomere shortening and chromosomal instability in the background and normal control with excessively shortened telomeres. The data suggest that cancer arises from epithelial cells with short telomeres.