Complex sentence: He initially received radiation therapy as treatment, but by December 1994, the cancer had returned and metastasized; at that point, he went on hormone therapy, on which he remained over the next decade until the treatment ran out in March 2004.
Split into simpler sentences: He initially received radiation therapy as treatment, but by December 1994, the cancer had returned and metastasized. At that point, he went on hormone therapy, on which he remained over the next decade until the treatment ran out in March 2004.