There is provided a compound of Formula I ##STR00001## wherein X is a ring system; R.sup.1 is any one of a sulphamate group, a phosphonate group, a thiophosphonate group, a sulphonate group or a sulphonamide group; R.sup.2 is any one of a sulphamate group, a phosphonate group, a thiophosphonate group, a sulphonate group or a sulphonamide group; wherein when X is a steroidal structure and both of R.sup.1 and R.sup.2 are sulphamate groups, the steroidal ring system (X) represents an oestrogen; and wherein said compound is capable of inhibiting steroid sulphatase (STS) activity and/or is capable of acting as a modulator of cell cycling and/or as a modulator of apoptosis and/or as a modulator of cell growth. There is also provided a compound of Formula VIII ##STR00002## wherein R.sup.2 is any one of a sulphamate group, a phosphonate group, a thiophosphonate group, a sulphonate group or a sulphonamide group; and wherein said compound is capable of inhibiting steroid sulphatase (STS) activity and/or is capable of acting as a modulator of cell cycling and/or as a modulator of apoptosis and/or as a modulator of cell growth.