Pancreatic cancer actually has one of the worst survival rates; in the UK around 25% of people diagnosed survive past a year, with 5% living more than five years after diagnosis [0]. Chemo in those circumstances often has the effect of prolonging life while significantly decreasing the quality of life, and as such many people choose not to go through with it.

[0] https://www.cancerresearchuk.org/about-cancer/pancreatic-can...