One goal of the Cancer Genome Anatomy Project (CGAP) is to identify genes expressed during development of human tumors.
For example, you can compare the differential expression of genes in normal, precancerous, and malignant prostate cells:
The image above is an excerpt from:
Cancer Genome Anatomy Project (CGAP), Digital Differential Display, "Compare stages of prostate cancer" demonstration, July 21, 2000.
http://www.ncbi.nlm.nih.gov/cgi-bin/UniGene/ddd?ORG=Hs& Pool1=Normal:281&Pool2=Precancerous:282&Pool3=Malignant:283& Pool4=Control:162+235.