This depends on the pathology. If it is benign or borderline and you have surgery to remove it then the prognosis is excellent. If you have malignant phyllodes then prognosis depends on how big it is (over 5cm is higher risk), how high the mitotic rate is (over 10 is malignant, over 30 is higher risk), whether there is stromal overgrowth (higher risk) and necrosis (higher risk). If you don't have any high risk features then you probably have a 90% chance of surviving 10 years or more. If you have a lot of high risk features then it could be significantly lower than that. If it has spread the prognosis is very poor as there are no effective treatments.