I would get a second opinion. Any unexplained hard lump should be looked at very carefully. You may want to have a needle biopsy done, or a surgical excision, to see exactly what it is.
There are many things it could be besides cancer, such as a fatty tumor. But certainly cancer comes to mind any time there's an unexplained lump, and it needs to be ruled out definitively, which cannot be done through blood tests alone.