Erin,

I don't have any ideas about the fixation portion of your 
question about the breast tissue if it is critical to have the 
tissues processed overnight.  But there is a processing method 
that seams to clear away some the fat that is present in the breast 
tissues thus facilitating better sectioning from your paraffin block.  
In your processing schedule try alternating xylene for 
100% ETOH after your first 100% ETOH. I know it sounds 
bizarre, but it works.  I assume that you use xylene as your 
clearing agent.  It is great if you had an extra processor, 
a back-up perhaps that you can dedicate to processing fatty 
tissues.  As always, try test tissue first to see if this 
protocol will work for you.  The protocol is listed below.  The station 
times/temperatures and vacuum/pressure can be adjusted to your 
own personal laboratory procedures.

1.  Fixative
2.  Fixative
3.  70% ETOH
4.  95% ETOH
5.  95% ETOH
6.  100% ETOH
7.  Xylene
8.  100% ETOH
9.  Xylene
10. Xylene
11. Xylene
12. Paraffin
13. Paraffin
14. Paraffin
15. Paraffin

I hope this helps.  Just an idea. 

Donald G. Awbrey, HT(ASCP) QIHC
Electron Microscopy / Image Analysis
DonaldAwbrey@TexasHealth.org
donaldawbrey@hotmail.com
(817)-878-5647