We did a project on this subject last year.  I was planning on writing it up but you know....time is short.

1.  We found Ki-67, ER, PR, Myogenin, HMB45, Melan A, PCNA, CD15, Alk-1 and C-Kit show decreased staining if stored at room temperature for six (6) weeks compared with sections cut from the same block on the same day and stored in the freezer.  Her-2 Neu is shows decreased staining  over longer time periods of about 2 to 3 months. 

2.  The room temperature was at 70 C. The decrease in staining was seen at approximately four (4) weeks.  It did vary from antibody to antibody.  

3.  We have carried the testing to six (6) months on those kept in the freezer and result thus far show good staining on all those listed .

4.  We routinely cut all our controls in batches.  They are tested, first and last sections, then are boxed and stored in the cold room until needed.  We find controls can be cut in slow times, stored and used for months without any staining problems.

5.  We harvest tissues in bulk so the same tissues are used over an extended period of time so any variations are noticed before major problems occur.