The fibronectin isoform containing the ed‐b oncofetal domain: A marker of angiogenesis

Different fibronectin (FN) isoforms are generated by the alternative splicing of 3 regions (ED‐A, ED‐B and IIICS) of the primary transcript. The FN isoform containing the ED‐B sequence, a complete type‐III‐homology repeat, while having extremely restricted distribution in normal adult tissues, reveals high expression in fetal and tumor tissues. Using the monoclonal antibody (MAb) BC‐1, specific for the FN isoform containing the ED‐B sequence (B+·FN), we demonstrate here, using immunohistochemical techniques, that while this FN isoform is undetectable in mature vessels, it is highly expressed during angiogenesis both in neoplastic and in normal tissues, as in the case of the functional layer of endometrium during the proliferative phase. B+·FN is thus a marker for the formation of new vessels, and the BC‐I MAb may be a useful reagent for evaluating the level of the angiogenetic process in different neoplasms.