Sounds like you're doing what i used to do - summarizing unnormalized healthcare/oncology data. If you can either normalize your underlying tables or create a stored procedure or view to do it, and use that in your report, your life will be a LOT easier.

I was in a situation like this, and once I bit the bullet and did some programming voodoo to crank out normalized views, the rest was easy. Performance was still terrible, but a "slow" query is faster than a person almost any day...

Can you post your data structure? This just reeks of a really bad underlying design. The whole "4 tables" thing worries me. Once I fixed the mess I was in, I had all the symptom data in one table, and a related "categorization" table, and my summarizing problems went away completely. So your predicament seems eerily familiar...