For those tempted to say "Oooooh, that was a work, he never had leukemia in the first place, he didn't lose hair, bla, bla bla....":
There's a possiblity that Roman actually was diagnosed with hairy cell leukemia, which is pretty much like winning at the lottery in the sense that a short round of treatment can easily cure it. So, it's very possible that after 4 months of treatment, he's getting closer to getting back in the ring.
https://www.cancer.gov/types/leukemia/patient/hairy-cell-treatment-pdq