A doubt in the terminology of sample size calculation

#1
Hi all,

While going through a published article of a clinical trial in cervical cancer, I came across this statement under statistical considerations.

"The study was designed to have a sample size of 110 patients with power of at least 80% (one-sided, alpha = 0.05) to detect differences in the hazard ratio of 1.5–1.6, with an assumed baseline survival of 5 years from randomization."

What is meant by "with an assumed baseline survival of 5 years from randomization". How exactly this sample size calculation is done?

Thanks in advance.