Intercellular communication within the tumor microenvironment plays a major role in the initiation and progression of cancer. It has been proposed that mitochondria and mitochondrial metabolism are crucial in these processes and that the transfer of functional mitochondria from stromal cells to cancer cells leads to the recovery of OXPHOS metabolism in cells with damaged mitochondria, thus helping restore their tumor-initiating ability. Mitochondria transferred via tunneling nanotubes (TNTs) were shown to alter the metabolism of recipient cells. This process has been reported between cancer cells, as well as between cancer cells and normal cells within the tumor. Therefore, a better understanding of this process is an important area of interest in cancer cell biology and cancer therapy.