Recent developments in nano and biotechnology enable promising therapeutic nanomachines (NMs) that operate on inter- or intracellular area of human body. The networks of such therapeutic NMs, body area nanonetworks (BAN2s), also empower sophisticated nanomedicine applications. In these applications, therapeutic NMs share information to perform computation and logic operations, and make decisions to treat complex diseases. Hence, one of the most challenging subjects for these sophisticated applications is the realization of BAN2 through a nanoscale communication paradigm. In this article, we introduce the concept of a BAN2 with molecular communication, where messenger molecules are used as communication carrier from a sender to a receiver NM. The current state of the art of molecular communication and BAN2 in nanomedicine applications is first presented. Then communication theoretical efforts are reviewed, and open research issues are given. The objective of this work is to introduce this novel and interdisciplinary research field and highlight major barriers toward its realization from the viewpoint of communication theory.