VARIABILITY OF IMMUNOHISTOCHEMICAL REACTIVITY ON STORED PARAFFIN SLIDES

Aims-To investigate the effects of slide storage on immunohistochemica l staining, since recent reports have indicated that storage of unstai ned paraffin slides far up to 12 weeks may lead to false negative immu nostaining of tumour markers. Methods-11 antibodies (anti-cytokeratin, epithelial membrane antigen (EMA ), vimentin, smooth muscle actin, PS 100, chromogranin, CD45, CD20, CD3, CD30, and oestrogen receptor (OR)) were tested on unstained paraffin slides of breast carcinomas, lympho mas, and neuroendocrine tumours that had been stored for three to 10 y ears. All the paraffin blocks were recut less than one week before imm unostaining. Immunostainings of years old slides were compared with th ose of recent slides in at least five cases for each antibody. For thr ee antibodies (anti-chromogranin, anti-CD3, and anti-OR) we also teste d one year old and three months old slides. Results-Intensity of stain ing on years old slides was strikingly reduced for chromogranin and CD 3 in several cases and was slightly stranger for vimentin. In some cas es a significant decrease of OR positivity was observed after three mo nths storage, and a complete loss of OR immunostaining after 12 months , No significant difference was noted with the other antibodies. Concl usions-Immunohistochemical detection of some antigens located either i n the nucleus, in the cytoplasm, or on the cytoplasmic membrane could be impaired by storage of paraffin slides as short a time as three mon ths. One should be cautious of doing retrospective immunohistochemical studies on stored unstained slides.