$re = '~adm-list-table-cell.*?\K[/ ]*(<span class="del".*?</span>)[/ ]*~';
$str = '<td class="adm-list-table-cell align-right"><a href="iblock_element_edit.php?IBLOCK_ID=1&type=news&ID=2&lang=ru&find_section_section=-1&WF=Y" title="title">2</a></td><td class="adm-list-table-cell align-left adm-list-table-cell-last"> / / / / <span class="del">ALL</span> / / / / / / / / / / </td>';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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