Inhibition of tumor growth by zinc depletion of rats.

Tumors grow less rapidly when implanted into zinc-deficient rats. The objective of this study was to determine if tumor growth is also inhibited when tumors first are established and then a zinc depletion initiated. Therefore, rats with palpable mammary adenocarcinomas or with sham implants were pair-fed either a control or zinc-deficient diet for 32 days. Rats were then killed and tumors, plasma and several tissues analyzed. In three separate experiments tumor growth was inhibited 32, 35 and 35%, respectively. The extent of tumor necrosis and tumor zinc concentration were not different between control and deficient groups. However, there was a significant positive correlation between tumor zinc concentration and percent viable tumor tissue in both groups. Although zinc depletion in tumor-bearing rats resulted in a 10% loss of carcass weight, there was little effect on liver, kidney and heart weights. As a result of depletion alone, zinc concentrations decreased only in plasma and kidney. As a result of tumor growth alone, concentrations of liver zinc increased and kidney copper decreased. In plasma of tumor-bearing rats, levels of zinc decreased 40% while copper and magnesium increased 50 and 13%, respectively. To our knowledge, this is the first demonstration that growth of established tumors can be retarded solely by dietary zinc depletion.