$re = '`([^,()\s][^,\n]*)\s\(`m';
$str = 'Topic 1 (Speaker 1)
Event_type_1 - , Topic 2 (Speaker 2)
Event_type_2 - , Topic 3 (Speaker 3)
Topic 4 (subtopic 1) (Speaker 1)';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php