49-year-old male noticed since several months a slowly-growing, firm mass at the angle of the jaw.
- A well-circumscribed tumor with peripheral normal parotid gland tissue is seen at low-power view. The tumor is surrounded by a thin fibrous capsule which is partly penetrated. The heterogeneous make-up of the tumor with areas of varying cellularity is characteristic.
- The tumor consists of dark, cuboidal epithelial cells forming strands, sheets, acini and tubules. The latter display a homogenous, eosinophilic content. Small spindle cells emerge from solid epithelial structures.
- Epithelial elements are blended together with a loose often myxoid connective tissue stroma. Islands of bone and cartilage are observed.
- The normal parotid gland tissue consists mostly of serous acini with basophilic cells and ducts lined by brightly eosinophilic cells within a loose stroma containing numerous adipocytes.
The pleomorphic appearance of this tumor with a seeming mixture of epithelial and mesenchymal elements conferred the name mixed tumor of salivary glands. Immunohistochemical evidence points to a myoepithelial origin of all cellular elements, also those of the stroma.