Has Anyone Heard an Explanation For Falling Ca125?

I had a CA125 of 110 before a stage 1C Endometrioid adenocarcinoma was removed on Feb 9th. On March 30th my CA125 was 28 and on April 22nd it was under 6. Has anyone else experienced this (without treatment besides surgery) and has anyone had a doctor explain why it would happen, especially since a 1C staging indicates that some microscopic disease can remain. I'm asking because my oncologist said I'd need a lot of cancer to make it go up. I didn't get an answer as to what would make it go down.