Malignant tumor removed surgically from sigmoid colon, the dr. said he found a very tiny mass on the uterus (millimeters) which didn't appear in ct. is this considered as metastasis or still stage 3?

Depends: The doctor should be able to tell you whether the uterine tumor was the same tissue as the colon or uterine was the mass on the uterus malignant as well? So, it could be metastasis or a benign separate tumor. Her doctor should be able to give more details. Good luck with her treatment.

Depends: Was the small lesion on the uterus colon cancer? Was it attached to the colon cancer itself? Was a hysterectomy needed? If it is a separate cancerous nodule, then yes it would be metastatic disease, stage 4. You need to go over all the findings carefully with the surgeon & medical oncologist, who may need to review all the findings with the pathologist to determine the best treatment choices.

Uterine mass: Did he take a biopsy of the mass? The only way to really know is to biopsy it. Otherwise, it's a matter of guess.

Was the mass on: The uterus which touched the sigmoid colon? Was this mass biopsied? More information would be useful. If biopsied and found to be consistent with colon cancer, the uterus is not a distant organ, but would raise the t to t4b and overall stage would become stage iii c.