Adenoid Cystic Carcinoma; A Review of Recent Findings.

We reviewed the recent findings of adenoid cystic carcinoma: clinical characteristics, histological features, prognosis, differential diagnosis and therapy. Nextly, to determine whether and how the histological features of the tumor varied during its natural history, we examined all the available histological slides from the same patient. We also investigated the origin of the tumor and the degree of differentiation immunohistochemically, and we estimated its proliferative activity by analyzing the nuclear DNA content.1) Adenoid cystic carcinoma is a common malignant tumor which arises usually in salivary glands, especially a minor salivary gland, and occasionally in a nasal or paranasal cavity or external auditory canal. It is characterized by insidious invasion, by proneness to perineural infiltration and by a mixture of several histological patterns in the same tumor. It often metastasizes to the lung hematogenously and occasionally invades the brain directly.2) The dominant histological pattern shifts from the tubular type through the cribriform and trabecular types to the solid type during the clinical course.3) Tumor cells stained positively for both the acinar-ductal cell line (lactoferrin, lysozyme, secretory component, CEA, amylase, keratin) and the myoepithelial cell line (actin, myosin and S-100 protein).4) The mean incidence of over 4.5 C polyploid cells in the regions with the dominant pattern in each tumor was lowest in that with the cribriform pattern, higher in trabecular pattern areas and highest in solid pattern areas. These results show that proliferative activity is lowest in the cribriform, highest in the solid, and intermediate in the trabecular pattern areas.The results of the present study may be of value in predicting the histological transformation of the tumor, estimating its prognosis and determining therapy.