As far as I understand there is couple of ways cancers are linked to insulin. Not necessarily insulin resistance but think in terms of things that cause insulin resistance also help cancer grow.
For me the most compelling connection is that people who are likely to develop insulin resistance are also people who are very likely to have relatively little autophagy. Autophagy is a process where your body consumes protein that already exists in your organism. It will consume all sorts of stuff and what is really important is that it will break down abnormal protein like protein that got misfolded.
Autophagy is promoted when you fast for at least 14-18 hours -- but people who are constantly eating when they don't sleep don't ever reach fasting this long.
It is crazy to take a look at how different people look after losing a lot of weight depending on what kind of route they chose. People who lost weight due to intermittent fasting rather than calorie restriction tend too look much better and have much less loose skin. What happens is, due to IF regime their bodies were regularly undergoing autophagy while they were on IF and during autophay they were essentially "eating" their own protein like unnecessary connective tissue, skin, etc.
Without autophagy to periodically clean garbage from your body various unnecessary things just lie there and cause all sorts of mayhem and inflammation. Misfolded protein is potentially carcinogenic because defects in those protein are pretty much random and if a protein gets broken just right it might be causing damage to pretty much anything else. It increases your chance that a random damage can start cancer going somewhere.
Another way insulin might be linked to cancer is that insulin is a growth hormone and cancer is a tissue with abnormal growth. I don't know the details and I know enough to say that insulin does not necessarily cause growth of everything (how fun it would be to get your ABS just by overeating...) But it seems really possible that if cancer is sugar-loving tissue that needs lots of it to grow and insulin tells your cells to take as much sugar from bloodstream as they can then cancer might "be loving it". And also there are some cancer treatments that rely on starving or at least slowing cancer growth with a high ketone and low sugar levels.