<?php
$string = "Dados do Usuário: JOAQUIM DE OIVEIRA, NASCIDO EM 2010, FORMADO EM: DIREITO, HOBBIE: FUTEBOL";
preg_match("/^([^:]*:\s)(.*)/", $string, $pedacos); echo $pedacos[2];
PD9waHAKCiRzdHJpbmcgPSAiRGFkb3MgZG8gVXN1w6FyaW86IEpPQVFVSU0gREUgT0lWRUlSQSwgTkFTQ0lETyBFTSAyMDEwLCBGT1JNQURPIEVNOiBESVJFSVRPLCBIT0JCSUU6IEZVVEVCT0wiOwogICAgcHJlZ19tYXRjaCgiL14oW146XSo6XHMpKC4qKS8iLCAkc3RyaW5nLCAkcGVkYWNvcyk7CiAgICBlY2hvICRwZWRhY29zWzJdOw==