It depends. MyCityofHope is built on the FollowMyHealth™ Universal Health Record product. If your other portal(s) also uses FollowMyHealth, then yes, you can simply add City of Hope to your portal and have access to both. If not, you would have two separate portals.
If your existing portal is also a FollowMyHealth portal, when you enter your email address to register a message will display if that email is linked to an existing account. If so, log in to your existing portal account and add City of Hope as a provider to be linked to your City of Hope health information.
Also, please note your demographics, such as name, address, insurance and preferred pharmacy, is downloaded the first time a FollowMyHealth account is created. If you have previously enrolled with another health institution that uses FollowMyHealth, the demographic information will reflect the information provided at that time.