Immunohistochemical detection of progesterone receptors in paraffin sections. A novel method using microwave oven pretreatment.

The benefits of microwave oven pretreatment of formalin-fixed routinely processed paraffin sections were assessed using citric acid solution to demonstrate progesterone receptors (PR). Parallel frozen and paraffin sections from 25 cases of breast cancer were stained with the PR-ICA kit (Abbott). Compared with untreated paraffin sections a great enhancement of PR immunostaining occurred after microwave irradiation. In 21 cases the percentage of positively stained tumor cell nuclei in microwave oven-pretreated paraffin sections was practically identical to that in the frozen ones. After microwave irradiation the PR score in paraffin sections was in three cases higher than in the frozen material. In comparison with the frozen sections, only one tumor of 25 showed a lower percentage of stained malignant cells after the irradiation. It is concluded that microwave oven pretreatment is a simple, reliable and reproducible method to detect PR in routinely fixed paraffin-embedded tissues.