Secondary Bone Cancer/Unknown Primary

I have been diagnosed with Adenocarcinoma. It was discovered via an MRI of my lumbar area for a possible ruptured disc. They have checked everywhere for my Primary Cancer and thus far have not found anything. I had a disc removed in my neck c6/c7 in 2001 and a donor bone was placed as a spacer. This area is "lit" up in my bone scan and I am just wondering if anyone can tell me if it is possible that the donor bone used could have contained active Adenocarcinoma cells and this be from whence my problem came? I know my type of cancer is "glandular based" but all of the areas in my body that normally have the primary cancer appear cancer free. Anybody got any thoughts or info??? Thanks!!!