I think yes and it depends on other things too. My mother died of colon cancer that eventually spread to her bladder, vaginal wall, uterus, etc., she wasn't in pain, or at least she never complained of any, she was in hospice in the end.
My father has had 5 cancers in 12 years, he has experienced miminal pain, he's had lung twice, had the left one removed, had bladder, prostate, and just recently colon.
His brother had prostate 7 years ago, and recently they found out he has bone, bladder and possibly colon, he is in pain now and takes percocet for the pain, he was just recently diagnosed.
My dad's brother in law was just recently diagnosed with advanced brian cancer, he doesn't have any pain just memory loss, tingling, inability to walk, etc.,
I just had colon surgery in March, I was diagnosed with Stage IIA colon cancer at 28, I had my entire large intestine removed, I've experienced bone pain from the chemo, the cancer pain was just in the side of my abd on the right.
I think everyone is different, personally and some people don't react the same. Out of 8 people in my mom's family 6 have had cancer, 4 are dead from it, all but 1 was in pain.
As far as him refusing treatment, my father is similar, he is 71. In my opinion, as a cancer patient and a caregiver of him and my mother, I think that is a sense of control for them/us, it's one thing they can control. Some people chose to ignore the symptoms, regardless how painful because the thought of finding out more is more painful and scary to them. It's very frustrating, depressing and an even overwhelming since of helplessness when you find out your have a life threatening illness. People often say to me when they find out, oh, that's so random at your age, but then again you could go out here and get hit by a bus, I hate that response for the simple fact that getting hit by a bus IMO is an infinite thing, it may or may not happen, having cancer is definitive, it's in my body, invading me, this is a reality for me, getting hit by a bus isn't. You know what I mean? I know they mean well but I totally don't put that on the same plain. It's almost like a mind f*ck because you can't do shiat but what they advise or suggest you to do.
My uncle feels similar to the pain issue, a lot of older folks feel that it is sort of normal to be in pain, but it isn't, it's hard to get that across, and no one should be in pain.
My advice to you would be to make sure that your father in law is on top of his medical treatment, if he doesn't like their response, seek another opinion we get second opinions on our car, houses, etc., but seldom do for our health. Additionally, get to know his insurance company and what they do and don't cover, then lastly, keep a chart for himself, request a copy of every medical test they run, this way if he ever needs to go to the ER in the middle of the night, they have a history there and don't have to call millions of people to get caught up on what's what. I keep a chart for me and my father, it helps the docs out a lot, especially when I see about 5 different ones. Again, if he isn't happy with the results or medical treatment here, seek extra insight at Georgetown, John Hopkins or WHC. I went to WHC to have my surgery, at my age, if I had it done down here I would have had to have a colostomy bag, with having my entire large colon removed, however, I went up there and they were able to do a connection of the small intestine to the rectum, not to mention my scar is only like 8 inches long compared to sternum to pubis that some have.
Sorry to ramble and ramble, but I just wanted to share some info with you. I hope some of it is helpful. Sorry you and your family have to go through this.