Clone SP1 has been established to work
in formalin-fixed, paraffinembedded tissues. The presence of ER in breast
tumors indicates an increased likelihood of response to anti-estrogen
(tamoxifen) therapy. Staining patterns observed include: ER+ and PR+, ER+ and
PR-, ER- and PR+, and ER- and PR-. The SP1 clone is a high affinity rabbit
monoclonal. An in-house study showed that SP1 clone had 5 times more binding
capacity than ER clone 6F11 and 10 times more binding capacity than ER
clone 1D5. Studies also have shown that the SP1 clone is superior to 1D5 in
predicting survival. Excellent results can be achieved with antigen retrieval at
lower temperatures such as 80 or 95 degrees Celsius. The robustness of SP1 is
further proved by the fact that in some instances staining can be obtained even
without antigen retrieval. Thus, SP1 may prove of great value in the assessment
of ER status in human breast cancer.