ΔE 17.5, loose: different enough that you should pick on purpose. Mars Yellow is noticeably darker, much more saturated than Cadian Fleshtone.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Mars Yellow is noticeably darker, much more saturated than Cadian Fleshtone.
The same difference applies the other way round: Cadian Fleshtone is noticeably lighter, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Cadian Fleshtone on the colour wheel See Mars Yellow on the colour wheel
All matches: Cadian Fleshtone equivalents · Mars Yellow equivalents