The General Instruction of the Roman Missal states the following:
The priest may be assisted in the distribution of Communion by other priests who happen to be present. If such priests are not present and there is a very large number of communicants, the priest may call upon extraordinary ministers to assist him, e.g., duly instituted acolytes or even other faithful who have been deputed for this purpose. In case of necessity, the priest may depute suitable faithful for this single occasion. These ministers should not approach the altar before the priest has received Communion, and they are always to receive from the hands of the priest celebrant the vessel containing either species of the Most Holy Eucharist for distribution to the faithful. (GIRM 162)
When the GIRM says "These ministers should not approach the altar before the priest has received Communion" it doesn’t mean they cannot be in the sanctuary. However, it does mean that their role as "extraordinary ministers of Holy Communion must be correctly applied so as to avoid generating confusion." (The 1997 instruction on "Certain Questions Regarding the Collaboration of the Non-Ordained," 8 §1). For example, when extraordinary ministers stand too close to the celebrant at the altar and receive Communion before the priest, it can easily confuse their role as "extraordinary" ministers of the Eucharist with that of the priest, who is the minister of the Eucharist and the "sole dispenser of the mysteries for which they are preparing" ("Certain Questions," 2 §5). The 1997 instruction also states: "To avoid creating confusion, certain practices are to be avoided and eliminated where such have emerged in particular Churches: extraordinary ministers receiving Holy Communion apart from the other faithful as though concelebrants" (8 §2).