add_rewrite_rule(
    '^cases(/([^/]+))?(/([^/]+))?/?',
    'index.php?page_id=4&industry=$matches[2]&subcat=$matches[4]',
    'top'
);

add_rewrite_rule(
    '^cases(/([^/]+))?(/([^/]+))?/?$',
    'index.php?page_id=4&industry=$matches[2]&subcat=$matches[4]',
    'top'
);