My husband brother died posterior fossa tumor is it a hereditary tumor ? i am pregnant and i am very afraid that the child will not inherit it, as far as this cancer belongs to hereditary tumors?

You would be wise to consult with a clinical geneticist (med school, children's hospital). Only 5% of brain tumors have a genetic component and most of these arise as part of named genetic conditions. The babies risk of this or any other disorder can be defined so you can better plan for your future. I am sorry for your loss. This is the best way to get the answer you seek.

Many childhood brain tumors are indeed located in the posterior area of the brain, and some are hereditary. Would fully elaborate on your history with a Pediatrician, and your Obstetrician. The statistics do vary and genetic studies could be undertaken if necessary.