Estrogen Receptor (ER):

• Nuclear Marker
• Stain is reported as PERCENT STAINING OF TUMOR CELLS and STAIN INTENSITY (1+, 2+, 3+).
• 1% or greater nuclear expression in tumor cells is considered positive, and therefore eligible to receive hormonal therapy.
• CAP-ASCO recommendations are for <1 hr. from time of excision/biopsy to having a cut edge of tumor in 10% neutral bufferedormalin fixative.  Fixation window of 6-72 hrs.  These times should be noted in the pathology report (time of excision, time in gross room, and time in fixative).
• Negative staining results in biopsy material without an internal control should be repeated on the excisional specimen using blocks with both tumor and benign breast parenchyma.

Progesterone Receptor (PR):

• Nuclear Marker
• Stain is reported as PERCENT STAINING OF TUMOR CELLS and STAIN INTENSITY (1+, 2+, 3+).
• 1% or greater nuclear expression in tumor cells is considered positive.
• PR expression is a prognostic marker, and not directly used for eligibility to receive a specific treatment.
• PR expression without ER expression should raise significant concern that the ER and PR slides have been mixed up, or there is a problem with the ER assay.  Many scientists believe that ER expression is required for PR expression.

HER-2 Overexpression (HER-2):

• Membraneous stain
• Stain is interpreted by combining stain intensity and percentage of tumor involvement to classify as (0, 1+, 2+, or 3+).
• • 0 (negative) = No staining or cell membrane staining in <10% of tumor cells.
  • 1+ (negative) =  Faint membrane staining (partial membrane staining) in >10% of tumor cells.
  • 2+ (equivocal) =  Weak to moderate complete membrane staining in >10% of tumor cells, or strong complete staining in <10% of invasive tumor cells.
  • 3+ (positive) =  Strong complete membrane staining in >10% of tumor cells.
• CAP-ASCO recommendations are for <1 hr. from time of excision/biopsy to having a cut edge of tumor in 10% neutral buffered fomalin fixative.  Fixation window of 6-72 hrs.  Over-fixation is probably not a clinically significant issue practically, but given the absence of relevant IHC data and the highly regulated environment surrounding HER2 testing, f/u FISH testing for negative results (outside the fixative window) is necessary.
• Equivocal (2+) results should be followed-up with FISH testing, if IHC is used as the initial testing modality (most common).  Less than 1/3rd of equivocal cases show Her2 over-expression by FISH analysis.

References