If a person is infected with hpv without symptoms, and the virus remains in the body, how can male cancers be diagnosed or detected early?

By self examination or, in the case of oral infection, by periodic examination by your doctor or dentist. If you have had receptive anal intercourse with other men, ask your doctor about anal Pap smear. If not vaccinated against HPV, do that now; the vaccine prevents infection with the 9 HPV types that cause 90% of HPV related cancers and genital warts. But don't worry: all HPV cancers are rare.