Foetal antigen 2 (FA2) in the stromal reaction induced by breast carcinoma

An indirect immunoperoxidase technique was used to examine the distribution of foetal antigen 2 (FA2), a recently described basement membrane (BM)-associated antigen, in invasive breast carcinoma (n = 34), fibroadenoma (n = 5) and normal breast tissue (n = 5), and to compare its distribution with that of laminin and collagen type IV. In normal breast tissue, FA2 was detected in the intralobular stroma as a broad band around acini and ducts, but was not present in the interlobular stroma. In areas of carcinoma in situ, FA2 was present diffusely around and in close contact with the glandular elements, the staining being more intense than that found around normal glandular structures. Two distinct patterns of FA2 distribution were found in adenocarcinomas of the breast. In the fibroblast reaction type, fibroblast staining dominated, whilst in the stromal reaction type, intense and extensive staining of the surrounding stroma dominated. Significant correlation was found between the degree of fibroblast activity and the degree of anaplasia (p = 0.005). FA2 extracted from breast carcinoma tissue was shown to be immunologically identical to FA2 fractions extracted from second trimester amniotic fluid (AF). The Mr of FA2 isolated from AF was estimated to be 26 kD, whereas the Mr of FA2 extracted from breast carcinoma tissue was slightly higher. The apparent Mr under reducing conditions were higher and three bands ranging from 26 to 29 kD were seen. FA2 was found to be immunologically distinct from collagen types I, III and IV, laminin, fibronectin and fibrinogen. The increased production and widespread distribution of FA2 in breast carcinomas suggest that FA2 is involved in the stromal changes which occur in response to tumour growth and/or invasion.