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</a>  For the vast majority of primary malignant tumors, there are no known risk factors or family history. âThe thinking is that all malignant brain tumors are genetic in origin, even if thereâs not a family history or a mutated gene thatâs been passed on,â says Yong. âIn these cases, a random mutation occurring in any one of the brainâs hundreds of billions of cells could lead to brain cancer.â