Longitudinal analysis of mammary cancer multiplicity in chemoprevention studies

Background: The effect of chemopreventive agents on cancer multiplicity is of primary interest in animal studies. The nature of data collected from ch emoprevention studies may be analyzed by a longitudinal analysis of repeate dly measured cancer multiplicity data. Methods: We determined the number of mammary cancers over the entire follow-up period for varying doses of two chemopreventive agents. Longitudinal analyses were performed to model the n umber of cancers over different time intervals. Results: There was a signif icant increase in the number of cancers between six to seven weeks post-car cinogen administration in the control group. Varying patterns of cancer dev elopment were observed at different doses of chemopreventive agents includi ng a delay in onset of tumor growth compared to the control group. Conclusi on: Longitudinal data analysis complements traditional analyses by providin g detailed information regarding the effect of chemopreventive agents on th e pattern of tumor development throughout the follow-up period. Importantly some chemopreventive agents may delay time to appearance of mammary cancer s without causing a significant difference in cancer multiplicity.