How to calculate Increase from baseline

Hi again,
I have a spreadsheet that listed patient #, the tumor size, tumor number, and scan date. I wanted to capture the percent tumor incr/decrease from the baseline. Baseline will be the min date associated with that pt and tumor#. I thought I could use the pivot table to do this but it only gives me the % incr/decr from previous scan date. This is OK with pts who only have 2 scans, but problem with pts with more than 2. Example with pt#018 (sheet1; row 114-116). Spreadsheet attached.
Can someone help me to resolve this problem either with a formula or pivot table. I use Excel 2002 now. Thank you so much in advance!

Hi JieJenn,
Thank you for your help, but you missed out the second criterion which is the tumor #. Each pt. may have several tumors at different location, hence they are numbered to distinguish from each other and easier to follow progress. Your formula works as if there is only 1 tumor per pt. Thanks.