SELENIUM-ENRICHED GARLIC INHIBITS THE EARLY-STAGE BUT NOT THE LATE-STAGE OF MAMMARY CARCINOGENESIS

Previous work has shown that the efficacy of cancer prevention by sele nium-enriched garlic (Se-garlic) is primarily dependent on the action of selenium, Additionally, supplementation of Se-garlic inhibited the post-initiation phase of mammary carcinogenesis when it was given cont inuously to the animals, In this report, experiments were carried out in which treatment with the Se-garlic was started after carcinogen dos ing (DMBA or MNU) but was restricted to either the early or late stage of neoplastic progression, The results from these two models showed t hat a short-term exposure to the Se-garlic for 1 month immediately fol lowing carcinogen administration was just as effective in cancer preve ntion as the continuous exposure regimen (5 months), suggesting that t he Se-garlic may irreversibly alter the process of clonal expansion an d/or selection of transformed cells during their early stage of develo pment, Plasma and mammary tissue selenium levels essentially returned to basal levels at 1 month after withdrawal of supplementation. These observations imply that the outcome of cancer protection by short-term Se-garlic intervention was not due to a slow turnover, and therefore a lingering presence, of selenium in the target organ or in the circul ation, The above finding was in contrast to that of a second study in which Se-garlic was supplemented starting at 13 weeks after carcinogen treatment, With this protocol, the number of new tumors and the numbe r of new tumor-bearing rats found during the intervention period (week s 13 to 22) were not statistically different between the control and s upplemented groups, suggesting that Se-garlic had a minimal effect on the later stages of mammary carcinogenesis.