Unfortunately this is a difficult diagnosis, suggest you share this article with your questions to the oncologist, metastasis to organs and especially to lymph nodes usually makes this inoperable and 5 years survivals are in the neighborhood of 15 to 35%. Much will depend on the age and condition of the patient, this may be very hard to take but I have found with my cancer that facing the facts is a start to dealing with all that comes next. Suggest that prior to starting chemo, Ensure that you're eating well and getting exercise and drinking protein supplements like Ensure. At my first visit I asked my oncologist if I did not have any treatment at all how long would I have, He said 5 months and that was Stage 3b. Be prepared to ask all questions regarding adverse effects and what to do especially managing the diarrhea and/or constipation.

Prayers for your Dad
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6295185/#:~:text=The%205%2Dyear%20relative%20survival%20rates%20for%20T4%20colon%20cancer,6%2C7%2C44%5D.