Areas of expertise for Dr. Callahan include bladder cancer, thyroid cancer, and liver tumor. He is affiliated with Cooper University Physicians. Dr. Callahan accepts Blue Cross/Blue Shield, Coventry, and TRICARE, in addition to other insurance carriers. After attending the University of New England, College of Osteopathic Medicine for medical school, Dr. Callahan completed his residency training at Kennedy Memorial Hospitals-University Medical Center, Stratford. His distinctions include: Fellow of the American College of Osteopathic Internists; Silver Chalice Award, American Cancer Society, Southern New Jersey; and Philadelphia Super Doctors.