What Causes Difficulty In Speech & Urinary Problems?

My sister is just recovering from stage 3 cervical cancer. She was treated with chemotherapy, radiation and finally rods that were inserted inside vagina to deliver direct radiation to the tumor. With no sign of the cancer in the cervix we thought she was in the clear. Unfortunately she has now been diagnosed with a brain tumor on the frontal lobe. It is 4cm in diameter covering the left side of the frontal lobe and has a popcorn like texture.She is finding it difficult to speak and suffers from urinary problems. The doctors are trying to work out whether the tumor was in the brain first or vice versa. What difference does this make?