Fibrous adenomas are often described as "invasive" by the surgeon simply because they are difficult to remove from the cavernous sinus, carotid wall or optic nerve. As such many postoperative scans of fibrous adenomas show residual tumor in these areas, whereas most secretory adenomas are friable and allow complete resection.
Histopathology is a more objective measure of invasiveness. DA treatment does indeed predict some fibrosis.