Ultrastructural heterogeneity of lung carcinomas: Representativity of samples for electron microscopy in tumor classification

Histologic heterogeneity of tumors is a well-known phenomenon, which has been repeated studied at the light microscopic level. Electron microscopy has been advocated as an adjunct in classification of tumors which pose difficulties on light microscopic classification. However, in view of tumor heterogeneity, it might be anticipated that the problem of sample error could detract from the usefulness of electron microscopy in tumor typing. Ultrastructural heterogeneity of tumors has thus far not been systematically investigated. We performed an ultrastructural randomized and blinded study of superficial and deep samples of 44 resected lung carcinomas, tumors which are notorious for their histologic heterogeneity. Neuroendocrine and squamous differentiation, as well as adenodifferentiation, were assessed separately and semiquantitatively in each sample. Twenty-six tumors showed more than one type of differentiation in at least one sample. However, in only two cases did the main type of differentiation differ between the two samples. A further nine cases showed one predominant differentiation type in both samples, but a similarly pronounced second differentiation type in one of the samples. Thus, in terms of ultrastructural diagnosis, the two samples showed a major discrepancy in two of 44 cases, and a minor discrepancy in nine of 44 cases. We conclude that ultrastructural heterogeneity of lung tumors is a common occurrence, but that it only rarely leads to totally different ultrastructural diagnoses.