Table 2. The effect of Atm deficiency on the proliferative index of Apc^Min/+ tumors.

The signals were counted, with the observer blind to the genotype, from digital photomicrographs displayed on a computer screen. Only crypts that were clearly epithelial by H&E staining on adjacent serial sections were assessed. Apc staining was used to discriminate between tumor (negative staining) and non-tumor (positive staining) tissue. Cells from the poorly characterized “cap” of Apc-positive cells surrounding the lumenal edges of tumors were not included. Six tumors and adjacent hyperplastic tissue were analyzed per genotype. The p-values were calculated using Fisher’s Exact Test.

	Ki-67-positive cells/total (percent positive; 95% CI)
Tissue type	Atm+/+	Atm−/−	P-value
Hyperplastic	481/2163	424/1461	<0.01
	(22.2%; 20.5–24.1)	(29.0%; 27.7–31.4)
Tumor	749/2128	1175/2338	<0.01
	(35.2%; 33.2–37.3)	(50.3%; 48.2–52.3)