Immunostaining of Type IV Collagen and Smooth Muscle Actin as an Aid in the Diagnosis of Breast Lesions.

The immunohistochemical staining patterns of type IV collagen (TIVC) and smooth muscle actin (SMA) were studied in benign and malignant breast lesions in order to assess their usefulness in the differential diagnosis of difficult lesions. Eighty-six in situ breast carcinomas (8 with microinvasion; 1 diagnosed after immunostaining) and 58 invasive carcinomas, with associated benign lesions including 87 nonproliferative fibrocystic changes, 19 sclerosing adenosis, 17 atypical hyperplasias, 7 benign papillary proliferations, 6 radial scars, and 105 normal mammary tissue, were studied. TIVC and SMA were concomitantly positive throughout in 94% of benign tissues, in 16% of in situ carcinomas, but in none of the invasive carcinomas.