We have used human specimens and antibodies to pERK1/2 to detect early development of colon cancer, using indirect immunocytochemistry. Two distinct sites were stained; one at the tip of the colon villi and the other in the stromal tissue, associated with the colon tissue. These foci represent early stages of colon cancer initiation, as established by enhanced KRAS, and lack of p53 staining. It should be noted, however, that the enhanced KRAS coincides with the initiation of tumor growth revealed by pERK1/2 only in the tip of the colon villi but not in the stromal initiation site of the colon tumors. Interestingly, foci of pERK1/2 staining were also detected within 50% of stromal tissue and tips of colon villi, that were classified as normal tissues, distal from the malignant one according to general morphology. The staining of pERK1/2 at the stromal foci of this apparently non-malignant tissue appeared as aggregates at the perinuclear region, while at the colon epithelium, it appeared at the cell nuclei. At low-grade of colon cancer, that was still free of induced mutated p53, staining of pERK1/2 was prominent at the cell nuclei both at the stroma tissue and the tip of the colon villi. In intermediate stage, that exhibited a significant p53 staining, only a fraction of p53-free tumor cells was labeled with pERK1/2 antibody, while in high-grade tumors, all cells of tumors were labeled with antibodies to p53, but not with pERK1/2. We also found that the cytoplasm of low-grade tumors was positive for epiregulin, while this labeling decreased in high-grade tumors. Interestingly, we found that the tumors initiating from the stroma demonstrated poor structural differentiation, while the tumors initiating from the epithelial cells of the colon demonstrated high structural differentiation. It is concluded that pERK1/2 is a sensitive early marker of colon cancer, which disappears at later stages of cancer development. Moreover, pERK1/2 staining can distinguish between tumor cells originated from the tip of the colon villi and those originated in the stroma, associated with the colon tissue, and thus can assist in selecting the appropriate therapy.