Morphological aspects of human malignant skin tumours. A freeze‐fracture study

Abstract

As a part of a systematic in vivo and in vitro study on epithelial skin tumours, freeze‐fracture investigations were carried out together with transmission electron microscopy and cell kinetics. The most important advantage of freeze‐fracturing in relation to the classical electron microscopical techniques is the visualization of membrane surface specializations such as nuclear pores, pinocytotic vesicles and particularly intercellular junctions. Biopsy material from keratoacanthoma (KA), nodular solid basal cell carcinoma (BCC), squamous cell carcinoma (SCC), Bow‐en's disease with invasive squamous carcinoma (BDC) and malignant melanoma (MM) was investigated. Cell and nuclear polymorphism with alteration of the nuclear/cytoplasmic ratio was observed in SCC, BDC and MM, while BCC exhibited a very homogenous size, shape and arrangement of the cells. The tumours commonly possessed interdigitation of their plasma membranes. Cytoplasmic organelles such as Golgi apparatus and lysosomal vesicles were highly developed in SCC and MM. In the latter, melanosomes, melanosome complexes and dendritic processes were impressive. Giant, lobulated nuclei were characteristic for SCC, BDC and MM. It could be established that – with the exception of MM, where no intercellular junctions were demonstrable – all tumours revealed various types of junctions, i.e. desmosomes, gap junctions and tight junctions, but so far no definite prevalence of the various functional structures could be demonstrated in these tumours. Nevertheless, desmosomes occurred regularly in BCC and also in SCC. Gap junctions were striking in SCC and KA; tight junctions were found in BCC, SCC and BDC. Pinocytotic vesicles could be demonstrated in all tumours with distinct differences in frequency and distribution patterns. In BCC pinocytotic vesicles appeared uniformly and closely arranged in great areas. In KA, SCC, BDC and MM they were more scarcely scattered in an irregular or patch‐like pattern. Nuclear pores were abundant in SCC and MM.