Detection by in situ hybridization of messenger RNAs of collagen types I and IV in murine mammary cancer

Ten breast carcinomas developing in C3H/Bi female mice were studied by an in situ hybridization technique using cDNA probes encoding α‐I chains of collagens of types I and IV. The results obtained are compared to histochemical data on antibodies to collagens of types I and IV and ultrastructural observations on these tumors. Immunohistochemistry has revealed the presence of type‐IV collagen in basement membranes lining intraductal and well‐differentiated cancer nests. Type‐I collagen was detected in the stroma surrounding these cells. There was no cellular labelling when these antisera were used. In situ hybridization has shown that type‐IV collagen mRNA is detected in non‐invasive intraductal and welldifferentiated tumor cells and in endothelial cells in the stroma. Good correlation between detection of type‐IV collagen lining these cells and evidence of mRNA by in situ hybridization was thus observed. Invasive cancer cells did not express hybridization grains with the type‐IV collagen probe. Type‐I collagen mRNA was visualized in stromal cells, probably fibroblasts and myofibroblasts as shown by electron microscopy. The most active cells were localized close to noninvasive areas. Our data indicate persistent in‐vivo biosynthesis of type‐IV collagen by some cancer cells that produce their own limitative environment; they suggest that type‐IV collagen is not produced by invasive tumor cells and that stromal cells lining the non‐invasive regions have a peculiar behavior.