The invention relates to novel compounds for use in the treatment or prophylaxis of cancers and other proliferative conditions that are for example characterized by cells that express cytochrome P450 1Bl (CYP1B1) and allelic variants thereof. The invention also provides pharmaceutical compositions comprising one or more such compounds for use in medical therapy, for example in the treatment of prophylaxis of cancers or other proliferative [Conditions, as well as methods for treating cancers or oth- er conditions in human or non-human animal patients. The invention also provides methods for identifying novel compounds for use in the treatment of prophylaxis of cancers and other proliferative conditions that are for example characterized by cells that ex- press GYP 1 B 1 and allelic variants thereof The invention also provides a method for determining the efficacy of a compound of the invention in treating cancer.