The use of correspondence analysis in the assessment of morphologic changes during carcinogenesis

Correspondence analysis is a statistical technique originally developed for the analysis of frequency and contingency tables. It may also be successfully applied to the problem of the assessment of the characteristics of samples of cytological material. The present article describes the use of this formalism on feature data measured on urothelial cells in populations obtained from rats at different time points after exposition to a carcinogenic agent. After the application of correspondence analysis, the projections of the samples corresponding to the different time points onto the plane spanned by the first two factorial axes constitute a trajectory, preserving the time ordering. The locations of the projections of cell samples of untreated animals (controls) with respect to this trajectory suggest that two different processes inducing different morphological changes are at work: Early abnormal samples are characterized by a lower-than-normal value of nuclear stain content, whereas late abnormals are mainly characterized by a higher-than-normal nuclear stain value. It is shown that populations of selected atypical cells show less variation throughout the carcinogenic process than populations of randomly selected cells.