Thanks to all who responded.

Suggestions,

1. Antigen diffusion from the nucleus to the cytoplasm due to a delay in
fixation or high antigen level.

2. From research on ER and PR on the primates in tissue staining and
biochemistry assay. We documented both nuclear and cytoplasmic ER. With
the advent of antigen retrieval and sensitive detection systems, the
cytoplasmic staining is observed with 1D5 ER clone and the 1A6 PR clone.
I believe the staining is real. Depending on what time the biopsy is
taken (high or low estrous during the menstrual cycle) you may see
various levels of cytoplasmic staining.

3. We were having a blush of cytoplasmic staining as well. When we
called the manufacter of the antibody, they thought that what we may be
seeing is an expression of biotin in the sample itself. We notice that
this happens in about 5% of our cases. It will happen with aspirate
biopsies, and excisional biopsies as well. We use the Vantana stainer,
and find that by using a secondary blocking step, we can cut the
cytoplasmic staining down to a readable level.

4. I used to get a lot of cytoplasmic staining when I was using the
ER-LH2 clone and I was questioning my technique as well. Since then I
have switched to ER-6F11 clone from Novocastra and I longer experience
any cytoplasmic staining.