Identification of the genes that are specifically expressed in either
tumor or normal tissue is important for understanding
cancer biology. Using differential displays, we obtained one gene which was specifically expressed in normal tissue but is only rarely expressed in
carcinoma tissue of the human esophagus. The sequence of this gene was identical with
cystatin B, known to be one of the
cysteine-proteinase inhibitors, mainly inhibiting
cathepsin L. There is little information on the clinical significance of
cystatin B expression in human esophageal
carcinoma. We thus studied the
mRNA expression of
cystatin B in 45
tumor/normal pair specimens of the esophagus, using the semi-quantitative
reverse transcriptase polymerase chain reaction technique. The expression of
cystatin B in
tumor tissue was found to be markedly decreased compared with that of the corresponding normal tissue. The cases with a
tumor/normal ratio of less than 0.5 showed high frequency of
lymph-node metastasis and more advanced clinical stage as compared with those whose
tumor/normal ratio was equal to or more than 0.5. The decreased expression of
cystatin B protein in
carcinoma tissue was confirmed by immunohistochemical staining. Our study suggests that reduced expression of
cystatin B in esophageal-
carcinoma tissue is associated with
lymph-node metastasis and may therefore prove to be a useful marker for predicting the
biologic aggressiveness of human esophageal
carcinoma.