Clone SP2 has been established to work
in formalin-fixed, paraffinembedded tissues. The presence of PR 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 SP2 clone is a high affinity rabbit monoclonal. An
in-house study showed that SP2 clone had a much higher affinity as compared to
mouse monoclonals for the progesterone receptor. Studies have also shown that
the SP2 clone provides supplementary evidence to ER in predicting survival.
Excellent results can be achieved with antigen retrieval at lower temperatures
such as 80 or 95 degrees Celsius. The robustness of SP2 is further proved by the
fact that in some instances staining can be obtained even without antigen
retrieval. Thus, SP2 may prove of greater value than ER as a prognostic
indicator in human breast cancer.