Immunohistochemical demonstration of oestrogen and progesterone receptors:correlation of standards achieved on in house tumours with that achieved on external quality assessment material in over 150 laboratories from 26 countries

To investigate the sensitivity of immunohistochemical (IHC) assays for oest rogen receptors (ER) and progesterone receptors (PR) achieved by laboratori es on breast tumours fixed and processed in their own department, and to co mpare this with the degree of sensitivity they achieve on rumours circulate d as part of an external quality assessment (EQA) programme. Methods-On 10 occasions between April 1994 and June 1998, histological sect ions from breast cancers showing various degrees of expression of ER and PR were circulated for IHC staining to laboratories participating in the UK n ational external quality assessment scheme for immunocytochemistry (UK NEQA S-ICC). The staining of these rumours, in addition to that of tumours fixed and processed in the participants own laboratories tin house rumours), was assessed by a panel of four assessors, using the established UK NEQAS-ICC scoring system. For a selected assessment run, the degree of expression of participants in house tumours was evaluated by means of the semiquantitativ e quick score method. Results-Although the scores awarded for the staining of in house rumours we re generally higher than those awarded for the staining of UK NEQAS tumours , there was also a significant positive correlation between the two sets of scores. Using the quick score method of evaluation for one of the assessme nt runs, 17% of in house tumours were classified as having a high degree of ER expression. Of the remaining cases, a significant proportion initially classified as having only low or medium expression of ER were found to have higher expression when stained by the organising laboratory. The UK NEQAS- ICC centre's routine assay for hormonal receptors was found to be 90-100% e fficient in achieving optimal demonstration of breast tumours from over 150 different laboratories. Conclusions-The significant positive correlation between the results obtain ed on the UK NEQAS tumours and the in house rumours provides evidence for t he view that results achieved on EQA material are accurate indicators of in house laboratory performance. Although most laboratories adequately detect ed tumours with high receptor expression, a large proportion of in house tu mours classified initially by participants' staining as being of low or med ium ER expression had a higher degree of expression when stained by the UK NEQAS-ICC centre. The efficiency of the organising centre's routine INC met hod for ER and PR in optimally demonstrating participants in house breast r umours shows that variations in fixation and tissue preparation are not lim iting factors preventing a different laboratory achieving optimal demonstra tion.