Ks 17. E3 is a great way to differentiate benign frommalignant forms of tumours, such as those of themammary gland, and to separate myoepithelial cells(positive for K17) from luminal epithelium of differentglands (mammary, sweat, salivary, bronchial, tracheal,laryngeal, and esophageal). Only the cornifying areas andthe outer root sheath of hair follicles exhibit suprabasalstaining in the epidermis. Reactivity testing on cultured celllines: HeLa, A-431 Particularly found tumours are benignmammary gland tumours; the majority of malignantmammary tumours test negative for keratin K17.