Protein profiles of serum and tissue. Representative SELDI-TOF/MS spectra of normal colon tissue (FIG. 1A) on the NP20 chip and normal serum (FIG. 1B) on the IMAC30 (Ni) chip. The two spectra differ significantly and each produce a total of 40 to 60 peaks. The majority of the peaks are present in the specified range from 2 to 10 kDa. FIG. 1C Comparison of a typical colon tumor spectrum (above) and a normal colon spectrum (below) in the range from 3 to 4 kDa. The arrows point to the three differentially expressed peptides, subsequently identified as HNP 1-3. The three peptides are expressed in normal colon tissue and the expression is upregulated in the tumor samples. The three peptides are present in normal serum, but are present in higher concentrations in colon cancer serum. The average peak intensity for the three peptides were significantly lower in serum than in tissue.