Can you live 10 years with brain cancer with out treatment?

Depends on the type: Depending on the type of brain tumor your are considering the answer is yes. Low grade tumors are very slow growing and may be silent for many years.

Diagnosis?: Cancer means malignancy. When someone talks about "brain cancer" they usually mean glioblastoma or brain metastasis which are not survivable for that long. You can live with a low grade or a benign brain tumor but those are not referred to as "cancer". Need an exact diagnosis to answer your question.