2-[2-(Methylsulfonyl)ethyl]-1H-isoindole-1,3(2H)-dione-d4 is an intermediate used in the synthesis of Lapatinib-d7 Dihydrochloride (L175807), which is a labeled Lapatinib (L175800), a reversible dual inhibitor of ErbB1 and ErbB2 tyrosine kinases. Antineoplastic.