Double immunolabeling with cytokeratin and smooth-muscle actin in confirming early invasive carcinoma of breast

Histopathological identification of invasive breast carcinoma in its earlie st phases is fraught with pitfalls. Preinvasive malignant lesions complicat ed by radial scar, sclerosing adenosis, and lobular cancerization, among ot her lesions, may simulate invasive carcinoma. Fibrosis, inflammatory reacti on, and other stromal changes around in situ carcinoma may mask microinvasi ve foci on routine stains. Conventional immunohistochemistry to demonstrate basement membrane or myoepithelial cell, layer may not, by itself, be uneq uivocally diagnostic of invasion. Wt performed a novel double immunoenzyme labeling technique using an avidin-biotin complex peroxidase-diaminobenzidi ne system for smooth-muscle actin followed by an alkaline phosphatase anti- alkaline phosphatase-new fuchsin system for cytokeratin antigen on formalin -fixed, paraffin-embedded histology sections to evaluate 32 such problemati c cases. The initial histologic impression with hematoxylin and eosin stain ing alone was as follows-first group: microinvasive carcinoma-10; second gr oup: carcinoma in situ-"stromal invasion cannot be ruled out''-15; third gr oup: frankly infiltrating carcinoma of various grades and morphologic types -6. The last group served as positive control for invasion. One fibroadenom a with fine-needle-aspiration-induced artifact simulating stromal invasion was also included. The double immunoenzyme labeling technique imparted a da rk brown color to the myoepithelial cells and a vivid red color to the epit helial cells, making individual or loosely cohesive groups of malignant epi thelial cells infiltrating the stroma easily detectable, whereas their in s itu counterparts were contained within dark brown myoepithelial boundaries. The TNM 1997 definition of pT1mic, i.e., extension of malignant cells in t he stroma with no focus measuring >0.1 cm, was followed to classify microin vasion. in the first group, microinvasion was confirmed in sis cases but wa s not demonstrable in four. In the second group, definite invasion was iden tified in five cases, ruled out in nine, and in one case the suspicion of e arly invasion could not be entirely ruled out even after double immunoenzym e labeling. Thus, it was possible to render a definite opinion regarding pr esence or absence of invasion in 24 of 25 (96%) cases diagnosed as or suspe cted to be microinvasive. The precise and simultaneous elucidation of topog raphy between malignant cells and myoepithelial cells on a single permanent section makes this technique a useful diagnostic tool in the evaluation of those cases of breast carcinoma that exhibit equivocal invasion.