As I have understood the various statements -
Jan - She had serious abdominal surgery, but it was not thought to be cancerous, although there would be a significant recovery period.
End Feb - In depth biopsy results showed that there had been cancer present - which I interpreted as having been removed during the surgery.
March - Catherine announced that she is having chemo - which I assume is to mop up any stray cancer cells that remain in her body.
She and William - quite rightly - took time to get their own heads around the situation, and keep their DC aware of what was happening, before she made the announcement yesterday. Totally reasonable.
Where all of this 'KP lied' rubbish comes from, I just don't know.
Wish Catherine speedy and effective treatment, and send love to the whole family. Very best wishes to all of our families who have been or are still being affected by cancer.