Influence of fixation, embedding and section mounting on stereological estimates of cancer cell mean volume-weighted nuclear volume

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Abstract

Objective malignancy grading of tumours by stereological estimation of the mean volume-weighted volume of cancer cell nuclei (V_V(nuc)) might be clinically useful. Prior to introduction in routine pathology, however, the effect of variations in tissue processing should be investigated. In the current study, the effect on V_V(nuc) was assessed in 27 breast cancers regarding variations in formalin fixation and embedding medium, whereas the influence of the mounting procedure was studied in 14 bladder tumours. For comparison, changes in gross dimensions of tumour specimens due to embedding were assessed in tissue from 5 breast cancers. Estimates of V_V(nuc) were stable regarding the duration and acidity of formalin fixation, but V_V(nuc) was, on average, 13% larger in methaciylate than in paraffin (2p=0.004). Mounting of paraffin sections directly from water provided a mean V_V(nuc) about 30% larger than standard mounting from xylene or mounting from ethanol (p</=0.02). The overall mean linear shrinkage of tissue bars in paraffin was 5%, whereas, in methaciylate, tissue bars swelled by 2% (2p>/=0.10). The dynamic changes in the dimensions of tissue were, however, dramatic during paraffin embedding (up to 15%), whereas methaciylate embedded tissue was much more stable (up to 5% change). Thus, for reproducible assessments of V_V(nuc), tissue processing should be standardized with respect to the type of embedding medium and the section mounting procedure. As paraffin embedding leads to great dynamic changes in tissue dimensions, the process is, most likely, sensitive, and should be strictly controlled. Mounting of paraffin sections from ethanol could replace routine mounting from the potentially toxic xylene without affecting estimates of V_V(nuc).

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Over : Morten Ladekarl

Over : Hans Svanholm