Is it ever that a brain tumour cause cancer elsewhere in the body?

Usually not: It is unusual for a brain tumor that originates in the brain(primary brain tumor) to spread elsewhere in the body. The most malignant adult brain cancer (glioblastoma-gbm) very rarely spreads elsewhere in the body. Some of the pediatric pnets may develop drop metastaces from the brain to the spine. That is, there may be seeds from these tumors that can be detected in the spine.