Rare cancer regressions have been reported after high fevers, acute infections, or fever-inducing treatments, so the idea has some factual basis. But the evidence mostly consists of case reports, historical series, and correlations, not proof that fever itself directly cures cancer. In modern medicine, hyperthermia is used as an adjunct to other treatments, not as a reliable stand-alone cure.
Caveats
Do not equate fever-associated remission reports with proof that fever alone caused the cancer to disappear.
Induced hyperthermia in oncology is not the same as an ordinary fever and is generally used alongside other treatments.
The claim omits how rare, unpredictable, and clinically unproven this effect is as a cure strategy.