First, I am sorry for your father’s diagnosis….stage 4 means that the cancer has spread and is in the lymph nodes, and requires systemic treatment …your post doesn’t say what tests have been done that would clearly indicate stage 4….at the beginning of my cancer journey, i still had many tests and imaging ahead and they said I had a large aggressive tumor, T4—I wrongly assumed I was stage 4–only my tumor was a 4 ! The beginning is hard, when info is far from complete…. Your father is blessed to have you by his side….wishing you both the best.