I’ve read the linked article now, and this is why I think your research is fine but probably not what we’re talking about here:
The princess’s statement explains that when she had abdominal surgery in January, it was not known that there was any cancer.
“However tests after the operation found cancer had been present. My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment,” said the princess.
The surgery would have been either a biopsy (relatively simple) or else taking out an internal tumor or organ with issues, which would have had (biopsy) testing done as part of the process. So technically she’s not lying when she says ‘it was not known’ on the day of the surgery. But the surgery was done because there was a serious concern.
And then, lo-and-behold, the biopsy testing found cancer. Which means the chemo isn’t preventative, it’s treatment. However, it’s true that she might ‘only’ have Stage 1 or Stage 2 cancer, in which case the chemo is to prevent it spreading elsewhere.
Basically, she’s trying to make it seem as innocuous as possible. But the truth is, she has cancer and there’s enough concern that they’re putting her on a course of chemo.
Which makes me wonder if the reason she’s been out of sight for so long might not be because there was some radiation therapy done to lessen the size of any cancer they found that was inoperable because of its location. That would explain a lot.