Complex sentence: Living Beyond Breast Cancer was founded in 1991 by Marisa C. Weiss, MD, a radiation oncologist, who was looking for resources and support for her patients who had completed treatment for early-stage breast cancer.
Split into simpler sentences: Living Beyond Breast Cancer was founded in 1991 by radiation oncologist Marisa C. Weiss, MD. Dr. Weiss was looking for resources and support for her patients who had completed treatment for early-stage breast cancer.