B2M and neoplasm: In contrast to the neighboring matched normal colorectal mucosa samples, COX-2 mRNA levels were overexpressed in 80%, 70%, and 40% of the colorectal tumor tissues, respectively, normalized with regard to tissue weight or the mRNA levels of the housekeeping genes B2M or GAPDH. The highest tumor/normal mRNA COX-2 ratios (mean ratio = 21.6) were seen when expressed per mg of tissue. Mean tumor/normal ratios were 16.1 and 7.5 when compared to the housekeeping genes B2M or GAPDH, respectively.