Disclaimer: I have zero medical training, just some experience dealing with my own pancreatic cancer and several relatives with other types of cancer.

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A lot depends on other aspects of your dad's health, whether the lesions are cancerous or not, exactly where they are on the pancreas, if a full-body CT or PET scan finds metastases elsewhere, etc...

If there are mets, they almost always rule out surgery and instead go with systemic chemo if appropriate.

If the lesions are suspected to be malignant cancerous tumors, a biopsy will probably be done to get tissue and determine the exact tumor type. That type of biopsy is often done during an endoscopic ultrasound (EUS) procedure under general anesthesia. It's rare but possible to get a false negative result from the biopsy; if that happens, they'll probably at least track the CA19-9 tumor marker, and order another MRI/MRCP or CT and CA19-9 test in 6-8 weeks to see if things have normalized or progressed.

If there is only one tumor, then the most common procedure to remove it from the head of the pancreas is called a Whipple procedure, or distal pancreatectomy (sometimes with splenectomy) to remove it from the tail. If it's in the body between head and tail, then it's totally the surgeon's call on how much to remove and (if any) what procedure to use. Whipple entails about a week in the hospital and 6-8 weeks of recovery at home.

If surgery would be too hard on him, radiation might be possible if the tumor is not in too sensitive a location, possibly in combination with a "mild" oral chemo pill called Capecitabine to provide some systemic control and help sensitize the tissue for radiation. If he is rather frail, then you might ask whether shorter durations of higher-intensity radiation would be better, or lower doses and spread out over time. Also ask if they have access to a proton beam or carbon ion radiation machine; these do less damage to surrounding tissue.

There are other less invasive and non-invasive methods of treatment, but no gold standards of any sort. TTF (Tumor Treatment Fields) is a small array of antennas in a wide belt you wear for 18 hours a day, ongoing indefinitely. If generates a low-frequency electromagnetic field that is supposed to disrupt the tumor's ability to reproduce. Basically zero side effects, but only seems to help when combined with some type of chemo.

IRE (Irreversible Electroporation) is another treatment that uses electric fields to kill tumor cells, but instead of dragging on for months, it's done one time in a surgical setting. They insert several (six?) "antennae" probes to build a "fence" around the tumor and then electrify the fence. I understand it can be done percutaneously or open; not sure about laparascopically. Percutaneous is far less invasive, but a bit more risky in terms of puncturing other tissue/organs when inserting the probes.

The Civa Sheet is one of several brachytherapy techniques to ask about. Brachytherapy is really a form or internal radiation. It would have to be done surgically, but doesn't involve cutting out any organs, so it's much easier to recover from than something like a Whipple procedure. The older techniques would put a radioactive pellet somewhere near the tumor and let it do its job. But the radiation can spread out in all directions and affect other tissue. The Civa Sheet is a newer technology that has multiple pellets on a sheet backed with gold to prevent radiation from escaping out the back. They basically just wrap the sheet around the tumor and let it go to work. I think the radiation decays first, then the sheet dissolves (iirc) afterward and doesn't have to be removed. (I could be wrong on this!!!)

Although you'd like to think the response to pancreatic cancer is like a TV episode of "House" where a whole team stays up 24/7 thinking about your case, the most likely outcome is a recommendation for "Standard of Care" therapy.

One thing to make sure of is that they're writing the treatment recipe for an 89-year old with Crohn's Disease, and not just for the mythical median patient.

For systemic chemo, they would probably avoid Folfirinox because of his age. They would probably go with Gemticabine if he can handle infusions (at least biweekly, maybe 3 weeks out of 4). They can add Abraxane and/or a platinum-based drug to that regimen, TBD by the docs. The platinum drug of choice is generally Cisplatin, but considering his condition and age, I would think a "milder" substitute like Carboplatin might be used instead. If infusions are ruled out, you should still ask whether they would consider oral Capecitabine.

My gut feeling is that a Whipple procedure would be pretty hard on your dad, and not really improve his quality of life. Similarly, my gut feeling is that anything beyond Gemcitabine alone for an IV would also not improve his quality of life much, but you know your dad better than I do, so a lot depends on how much energy and fight he has in his system, and how much longevity is typical in his family.

Genetic testing should be done as soon as possible to help steer his treatment.

I would look for clinical trials outside the Standard of Care arena as a first-line option to try and get the most bang for the buck -- a better response with fewer or less debilitating side effects.

Wishing you both the best!