The doctors think my grandpa's bladder cancer spread to his brain but how? he hasnt had bladder cancer in about 6 months. he does have cll leukemia

Probable bladder met: CLL usually remains dormant for long periods. Ive had several patients with bladder Ca with mets to brain. Prior to treatment of the primary bladder lesion which can control disease either by fulguration and or BCG some tumor cells may have invaded blood system. Cells in blood have reservoir in bone marrow and as such 6 mo. after primary treatment cells leave marrow to implant in brain