It depends on what you mean.
Usually people asking that question are implicitly asking: Which is the true Church?
Catholics say the true Church is that which is in communion with Peter, on whom Christ build the church. Peter’s historic successor is in Rome. So those communities in communion with Rome belong to the fullness of Christ’s Church.
So in this way, all particular churches that break communion with Rome (like Constantinople) are leaving the fullness of Catholic unity. And yet, these same particular churches may have had ancient — even apostolic — origins.
For example, the apostolic church of Antioch, whose origins are described in the New Testament, eventually broke communion with Rome. Depending on how you sort it out, this occurred as early as the early AD 400s, when the Syriac Christians followed Nestorianism, forming what became know as the Church of the East. Ever after, the Antiochene Christians more or less followed the Byzantine Greeks, which, too, would eventually lose communion with Rome after the Great Schism.
So the history is complex.
Now the Orthodox, in turn, generally see Rome as a particular church* that went into schism for various reasons, depending on who you ask. To be fair, at most you could say that Rome went into schism with Constantinople, and eventually the Byzantine (Constantinople)-based churches in communion with it.
But even from this view, Orthodox have to admit that the Roman church was in existence from apostolic times — just as Catholics have to admit that various Eastern churches that went into schism also existed from ancient times.
*All my use of “particular church” just means a community of Christians gathered around their head bishop. The bishop represents the church in local sense.