Could the size of a brain tumor have any significance whether its benign or malignant?

Typically not: The size of a tumor usually doesn't determine whether the tumor is benign or malignant. I've had patients with very large tumors that are benign and tiny tumors that are malignant. Whether or not a tumor is benign or malignant depends on what type of cells the tumor is composed of. Often the only way to determine this is with biopsy.