Ribosome-lamellae complexes in a symptomatic insulinoma. An ultrastructural study.

Ribosome-lamellae complexes (RLCs) were identified in approximately 20% of the tumor cells from a functional insulinoma studied by electron microscopy. Whereas these peculiar cytoplasmic inclusions are commonly seen in hairy cell leukemia (HCL) and can be present in a few cells in other hematologic disorders, to our knowledge they have never been documented in insulinoma. In fact, they are exceedingly rare in epithelial tumors. A review of the literature uncovered only two instances, one in an adenoma of the adrenal cortex, and one in a paraganglioma. In these two cases and in the insulinoma reported here, RPCs tend to be longer, have fewer lamellae, and occur in greater numbers per single cell than in HCL. Although the nature and significance of RLCs remain poorly understood, the fact that all three epithelial neoplasms in which they have been observed belong to the endocrine system is noteworthy.