Trust your gut.

[Mik]

Doctors are not always right.

https://www.msn.com/en-us/health/medical/mom-survives-colon-cancer-twice-shares-symptoms-doctors-dismissed-i-knew-something-was-wrong/ar-AA1gFmZp?ocid=msedgntp&cvid=6c81460ab5bf46d4a1ba8bd308a0716f&ei=20

[George K]

In 2017, life was normal except that I was having a lot of back pain. I went to the emergency room and a scan showed a lesion on my liver. A local gastroenterologist said it was nothing to worry about and said we’d check it in six months.

What kind of scan? An ER ultrasound?

I went to another doctor who said, “Let’s just go and do an MRI.” It turned out to be stage 4 colon cancer that had metastasized to my liver.

Any lesion should be investigated. "Don't worry about it" is not appropriate.

4 years later there's a recurrence. If it's so big that it grown into the pelvis, you'd think that routine surveillance would have found it. Also, her symptoms of painful gas, the feeling of not emptying your bowel should have been clues.

I'll wait for someone who knows more about this than me - like @bachophile , but it sounds like it was mismanaged all around.