Not logical at all! In my first round with PDAC and 6 months of chemo, the tumor never changed size much on MRI, but the meds were having some impact on it. After removal, pathology confirmed some of the tumor tissue was killed by the chemo. (So the "living" part of it shrunk a little bit.) But my CA19-9 numbers never really improved.

Since the recurrence and 4 months' treatment with a different chemo, the CA19-9 numbers are improving rapidly, but last week's MRI showed no reductions in size plus a possible new tumor. I had no symptoms when it was caught (still don't) and am tolerating the chemo very well.

Sometimes chemo before the surgery is used not only to treat the disease, but also to determine which patients may benefit from surgery. Even if a single, resectable tumor is not shrinking on MRI/CT, as long as it doesn't spread, they'll know it's treatable and responds to meds. Very often, pancreatic tumors have spread microscopically beyond what imaging can detect. Surgeons know this, and don't want to put you through surgery if it won't help in the big picture, especially since it would delay your resumption of chemo/immunotherapy after surgery. Distant metastasis will probably rule you (your Mom) out as a candidate for surgery, but stable or slight increase in tumor size at one site may not.

Wishing you and her the best!

Just curious: Do you have details on exactly what type of cancer it is, what the driving mutation/fusion is, and what drugs are part of the trial?