Low temperature antigen restoration of steroid hormone receptor proteins in routine paraffin sections

The most widely used non-enzymatic method for unmasking antigens prior to immunohistochemical staining is based on immersion of deparaffinized paraffin sections in citrate buffer and exposure to high temperature heating (100 degrees C) with a microwave. In our experience, the benefits of this technique as applied to cytoplasmic proteins does not routinely translate to the nuclear estrogen and progesterone receptor (ER and PgR) proteins. The lifting or loss of portions of a breast biopsy section can seriously interfere with efficient scoring of invasive tumor cells. The use of low temperature restoration (80 degrees C) in citrate buffer using a water bath avoids problems of tissue disruption and generally restores the immunoreactivity of ER and PgR proteins in a more uniform fashion than does the microwave approach.