Annulate lamellae in human malignant tumors: report of three cases.

During the course of applying electron microscopy to diagnostic surgical pathological specimens, three malignant tumors (malignant melanoma, fibrous mesothelioma, lymphoblastic lymphoma) were found to contain annulate lamellae, distinctive intracytoplasmic organelles composed of membrane stacks interrupted by constrictions or pores. In one case both annuli and lamellae were present, a combination rarely described in human tissue and in animal models. In this material, the annuli of the annulate lamellae were structurally similar to nuclear pores. It is postulated that the abundant fibrils are probably related to the unusual configuration of the annulate lamellae. A morphologic relationship of the annulate lamellae to both the endoplasmic reticulum (cases 1 and 2) and the nuclear membrane (case 3) supports the theory that annulate lamellae may be related to both of these structures.