If your dad has a lot of weight on him and a really POSITIVE attitude he should be able to handle treatment. The most important thing is keeping his weight up. If he starts losing alot of weight, the body seems to start giving up. And a person's attitude about life plays a very important role in how treatment is handled. Good luck to you and your Dad and God Bless you and your family.
I know this is difficult. My mom was diagnosed with stage 4 colon cancer in 2005. Her chances for surviving 5 years were less than 10%. She had some difficult times, but she lived to see 4 grandsons born. She just passed away last month, but she said she never regretted the things she got to see with the treatment. Like the previous poster said, maintaining your weight is very difficult. If he is very positive about the treatment, there's no reason not to try. Take care.
Sorry to hear about your dad. This week we just found out my father-in-law (age 60) has Stage III colon cancer. The doctors told him that he is a healthy guy (besides the cancer), so that will definitely help his chances of recovery. Is your dad in good health otherwise?