Table II.

Effect of Zn supplementation on tongue carcinogenesis in rats exposed to low doses (10 p.p.m.) of NQO for 8 weeks^a

Group (No. of rats at study conclusion)	Body weight (g)	Serum Zn levels (μg/100 ml)	Gross examination			Histologic examination
			Tumor incidence (%)			Preneoplastic lesions incidence (%)		Neoplastic lesions incidence (%)
			Total tumors	Tumors (1–2 mm)	Tumor multiplicity	Hyperplasia	Dysplasia	Papilloma	Minimally invasive SCC
Control (25)	493 ± 39	144 ± 6.7	25/25 (100)	9/25 (36)	8.6 ± 3.4	22/25 (84)	12/25 (48)	15/25 (60)	9/25 (36)
High Zn (26)	495 ± 34	176 ± 9.8b	26/26 (100)	2/26 (7.7c)	5.2 ± 2.3b	13/26 (50d)	5/26 (19e)	7/26 (26.9f)	3/26 (11.5g)

^aBeginning at age 6 weeks, male rats were fed a Zn-sufficient diet and received drinking water exposure to NQO (10 p.p.m.) for 8 weeks. The animals were taken off NQO and immediately given drinking water supplemented with 0 and 20 p.p.m. Zn to form control and high Zn group, respectively. The study was terminated 10 weeks after NQO cessation. Body weight, serum Zn levels and tumor multiplicity (number of tumors/tongue) are presented as mean ± SD and analyzed by unpaired t-test. Tumor and lesions incidence (number of rats with lesions/total number of rats) was analyzed by Fisher's exact test. All statistical tests were two sided.

^bCompared with control: P < 0.001

^cP = 0.019

^dP = 0.006

^eP = 0.040

^fP = 0.025

^gP = 0.052