Adenoid cystic carcinoma: A comparative pathologic study of tumors in salivary gland, breast, lung, and cervix

Histologic, histochemical, and ultrastructural features of eight adenoid cystic carcinomas arising at diverse sites were compared in order to determine diagnostic values and to investigate histogenetic mechanisms. These tumors originated in the salivary glands, breast, uterine cervix, and tracheobronchial tree. By light microscopy each tumor was seen to have morphologic features of adenoic cystic carcinoma, yet only five of the eight cases showed differential staining for the two mucin types, stromal and epithelial, which are reportedly present in these tumors. In contrast, every case showed a set of fine structural features which, in aggregate, are specific for adenoid cystic carcinoma. These features include pseudocysts, intercellular spaces, basal lamina, and true glandular lumens. The most prominent feature is the pseudocyst, which mimics a glandular lumen by light microscopy but is actually a rounded extracellular space containing basal lamina. Ultrastructurally, the variation in composition of the extracellular compartments, including pseudocysts and true lumens, appears to explain the lack of uniformity in the histochemical staining. The tumors also contained cytoplasmic microfilaments in parallel bundles, consistent with myofilaments. The presence of these filaments combined with basal lamina suggests myoepithelial differentiation, yet it is not known whether these tumors truly originate from myoepithelium or show differentiation toward myoepithelium as a part of the neoplastic process. Regardless of their histogenesis, this study shows that true adenoid cystic carcinomas do arise in different organs. Knowledge of the specific ultrastructural features of adenoid cystic carcinomas can be useful in classifying these tumors in some cases.