How long does paraneoplastic syndrome last if the entire tumor was removed and no further treatment is necessary?

Tough to know: The paraneoplastic syndrome is caused by an inappropriate immune response. The immune system was "allowed" to mount an attack on your body (sometimes attacking nerves, blood vessels, muscle, etc). Treating the tumor could result in a reset so that the immune system is rebooted, but this could take weeks to years and is highly dependent on specific factors that vary from person to person.