Remember, with cancer you have 2 basic situations:
1) Tumor, isolated (possible multiple tumor growths): Simply, the cancer is located in a mass, or multiple masses or the organ or tissue of origination, "easily" removed through surgery with a bit of chemo therapy to kill off any loose cells remaining. Based on manga, this is likely the situation she came across.
2) Metastasized: The cancer has "broken" off and and now crowing in more than one area of the body. Still the same cancer, but the cells are in various organs other organs and tissues. Due to this. surgery is only helpful for the large growths and you become much more reliant on the chemo/other for a cure. At this point, cancer is much more difficult to cure and have a much higher chance of failure. In some cases, once this has occurred, death is pretty much a foregone conclusion.