I have had that same thought a long time ago. Also, perhaps she even lied to Tiroy about the nature of the surgery. If she now reveals what that surgery was about and she had lied to Tiroy about it, then Tiroy and his entire family would know that she is a liar in that case.
Maybe she should have been having annual colonoscopy exams since that 'tummy/stomach' surgery which she obviously didn't bother doing. If she had had an annual colonoscopy, the tumor in her colorectal area would have been caught at the T1 stage or as a simple polyp and removed. Colon cancer starts as a polyp, and this can be confirmed from her very surgeon and other publications. Perhaps she lacked the follow-up exams on her part throughout the years. I still find it incomprehensible that when she was diagnosed, her tumor was already a T4bN1b cancerous tumor. Someone with stomach/intestine problems as she has had in the past needs regular screening. I highly suspect she is hiding something.
Her sister and her mom should also be having regular colon screenings. Just because a hereditary link wasn't discovered doesn't mean it doesn't exist! Research in that area is ongoing. It is not a coincidence that her aunt died of cancer, likely before her 50's.