I think you husband is in the same boat as myself. When they found my colon cancer through a colonoscopy it confirmed that I had cancer, but when they did blood work after that they could not find cancer.
My doctor told me I was one of the few people that cancer did not show in a typical blood test. I can not tell you for sure that he might also be one of the few ones as well, but I would ask your doctor more about this.
Since I have colon cancer a blood test for carcinoembryonic antigen (CEA, a substance produced by most colon cancers that circulates in the blood) if the numbers go up then further testing has to be done like a PET Scan. This is the way that my oncologist keeps track of my cancer, and to see if it is in remision or if there is a recurrence of it.
Unfortunately for me my numbers did go up after my last chemo treatment and so now I am scheduled for a PET Scan on Tues.
Goodluck to you and your husband. I know what you are going through. I am a single mother of three teenangers, 16 year old son, and two 15 year old twin daughters. My heart goes out to them because I know they are hurting too. I am all they have. I have been battleing colorectal cancer since July September of last year. I wish you two the best. I feel your pain.