Hi @kslayer, that is a good question for your relative's cancer team. I'm tagging fellow members like @stageivsurvivor @gamaryanne @susanpmadigan @ncteacher @lfitz, who I believe have experience with chemoradiation and 5FU.

You may also be interested in this related discussion.
- Radiation and chemo for pancreatic cancer: Is it effective? https://connect.mayoclinic.org/discussion/tadiation/

I can't speak for your family member's specific situation, but it is not uncommon to patients to be offered "chemo holidays" to recover from side effects without decreasing the effectiveness of treatment. Sometimes a chemo session may be delayed if one's blood cell count is too low. Adjustments may also be made to the chemo drug mixture if one of the drugs is causing a specifically challenging side effect. For example, reducing the amount of cisplatin if there is concern about permanent peripheral nerve damage.

As you can see, there are a variety of possible options that can be discussed with the cancer team to make sure the option is best for your relative, the goal of treatment and quality of life/side effects. It is an individual choice made with the medical team who have all the medical records, history, etc.

What side effects is your relative finding challenging at this point?