<unk>  is a drug used in chemotherapy.
It is structurally similar to lomustine, being distinguished from it only by an additional methyl group. It has been taken off the drug market for investigation of its cancerous effects, rated as IARC Group 1 carcinogen or a known carcinogen.
Semustine
Bendamustine
Lomustine
Zorubicin
Ifosfamide
Estramustine
Carmustine 
Fotemustine