Background Adenoid cystic carcinoma (ACC) is a biphasic salivary gland malignancy that is characterized by cellular, morphologic, and clinical heterogeneity. ACCs are the second most common salivary gland malignancy, are the most common malignancy of minor salivary glands, and comprise 15 to 25% of all salivary carcinomas. ACC arises from the intercalated ducts, which are composed of inner ductal epithelial and outer myoepithelial cell. The histogenesis of these tumors is uncertain. However, an origin from stem cells with multidirectional differentiation is likely possible. Histologic architecture alone determines the grade of ACC: tubular and cribriform growth patterns are associated with a longer survival time than solid forms are. We are currently starting to understand and get insights into intrinsic subtypes of this cancer directly linked to the dominant myoepithelial (M-ACC) or epithelial (E-ACC) cell type.
Methods The purpose of this study was to revisit outcomes of a cohort of 54 consecutive ACC patients treated at a single institution and classified according to their dominant cell type as E-ACC and M-ACC.
Results Follow-up ranged from 4 to 336 months. Of the 33 E-ACC patients, 17 (52%) were dead, 7 (27%) were alive, and 9 (21%) were alive with no evidence of disease at last follow-up. Of the 21 M-ACC patients, 3 (11%) were dead, 9 (37%) were alive, and 11 (52%) were alive with no evidence of disease at the time of the study. The proportion of living M-ACC patients (89%) was higher than the proportion of living E-ACC patients (48%). M-ACC patients had significantly better overall survival than E-ACC patients did (p = 0.00882). M-ACC patients also had better disease-free survival than E-ACC patients did, but this difference was not significant (p = 0.07048).
Conclusion Compared with E-ACC patients, M-ACC patients had better disease-free survival and significantly better overall survival, suggesting that ACC subtype has prognostic implications. Our study highlights the importance of subtyping ACCs according to their dominant histological pattern and dominant cell composition, as this is reflected in clinical outcomes.
