Wordpress UPDATE Query Syntax

I keep getting an error saying there is something wrong with my syntax at line two.  I'm using wordpress and not 100% sure how to do multiple updates to the wp_postmeta table:

$update_meta_item = $pdo->prepare("
						UPDATE wp_postmeta
						SET meta_value = :price WHERE meta_key = '_regular_price' AND post_id = '$prod_id',
							meta_value = :price WHERE meta_key = '_price' AND post_id = '$prod_id',
							meta_value = :quantity WHERE meta_key = '_stock' AND post_id = '$prod_id'"); 
					
					
					try	{
						$update_meta_item->execute(array(
						':quantity'=>$data[16],
						':price'=>$data[3])) or die(print_r($update_meta_item->errorInfo()));
						echo '<b>'.++$cnt .'</b> -- Product ID: <b>'. $title.' </b> has been updated.<br />';
						
						}
						catch(PDOException $aa) {
   							echo 'ERROR: ' . $aa->getMessage();
						}

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