Might it be that a a hip joint infection be a sign of cancer?

Only if chronic: Chronic draining sinus from infected joint can lead to squamous cell carcinoma.

Unlikely: Although a hip joint infection is quite a difficult problem it is not typically a sign of cancer. Hip joint infections can occur in a low percentage of hip joint replacements. They also occur in infants. Other than these two patient populations, this is a relatively uncommon problem.