An increasing amount of evidence indicates that a small extracellular
chondroitin/
dermatan sulfate proteoglycan,
decorin, is indirectly involved in angiogenesis. Given that angiogenesis is a sine qua non for
tumor growth and progression, we attempted to examine whether human malignant vascular
tumors differ from human benign vascular
tumors in terms of their
decorin expression and synthesis. CD31 immunostaining demonstrated that the human malignant vascular
tumors Kaposi's sarcoma and
angiosarcoma were filled with capillary-like structures, whereas in benign cavernous and
capillary hemangiomas, blood vessels were not as abundantly present. By utilizing in situ hybridization and immunocytochemical assays for
decorin, we showed that there was no detectable
decorin mRNA expression or immunoreactivity within the
tumor mass in the
Kaposi's sarcoma or
angiosarcoma group. Instead,
decorin was expressed in the connective tissue stroma lining the
sarcoma tissue. In contrast to
sarcomas, in
hemangiomas,
decorin mRNA expression and immunoreactivity were observed also within the
tumor mass, particularly in the connective tissue stroma surrounding the clusters of intratumoral blood vessels. Finally, distribution of
type I collagen was found to be similar to that of
decorin in these
tumor tissues. Our findings can be explained with different states of angiogenesis in dissimilar growths. In
sarcomas, angiogenesis is extremely powerful, whereas in
hemangiomas, angiogenesis has ceased. Thus,
decorin is likely to possess a suppressive effect on human
tumor angiogenesis in vivo, as previously described by studies using different experimental models.
Decorin certainly provides a usable
biomarker for distinguishing between benign and malignant vascular
tumors in patients.