Excessive deposition of extracellular matrix or neomatrix is a charact
eristic of desmoplastic invasive breast carcinomas. Type I and III col
lagens are abundant neomatrix components. Archival breast tissue secti
ons were studied using S-35-labeled cDNA probes for alpha 1(I) and alp
ha 1(III) procollagen and in situ hybridization. Among the 33 invasive
breast cancers, hybridization was seen forming a gradient-like patter
n in fibroblasts closest to tumor cells. In the 10 ductal carcinomas i
n situ studied, a ring-like pattern of hybridization was seen in proxi
mity to the basement membrane zone. Adjacent normal and benign tissues
did not demonstrate the patterns of hybridization described in malign
ant tissues. Gene expression for neomatrix interstitial collagens occu
rs before there is evidence of invasion in carcinoma of the breast.