Here are two published statements about the additional burden of cancer which might be due to recent increases in the prevalence of obesity:
“Overall, a 1 kg m−2 increase in body mass index (BMI) is associated with an approximately 1% increase in incidence for all cancers combined (based on data from women) and about a 2% increase in total cancer mortality (based largely on data from men).”
“We estimated that a 1 kg/m2 population increase in mean BMI would lead to 3790 additional patients in the UK each year developing one of the ten cancers that were overall positively associated with BMI.”
These two statements are entirely consistent. The “3790 additional patients” is just over 1% of the roughly 330,000 people diagnosed with cancer each year in the UK.
The real difference between them is in how they are framed. The first focuses on a small, dimensionless, relative increase, and the second on a seemingly large absolute number of unspecified but real, live patients. Ultimately, the statements refer to the same finding, but they are supposed to mean different things to the reader.