About Us

Backus Physicians

Backus Physician Services LLC, a practice affiliated with The William W. Backus Hospital, offers a wide range of minimally invasive surgeries for patients.

Four surgeons practice in the Norwichtown Medical Office Building at 12 Case St., Suite 313 – Sergio Casillas, MD, specializing in colon and rectal surgery as well as general surgery; Michael Deren, MD, specializing in thoracic surgery; Juan Escalon, MD, specializing in thoracic surgery; and Mark Tousignant, MD, specializing in general surgery.


Sergio R. Casillas, MD

Dr. Casillas is a member of the medical staff since 2004, is double board-certified in General Surgery and Colon and Rectal Surgery. He did his general surgery training at the State University of New York in Syracuse, New York, then specialized in Colon and Rectal surgery followed by a fellowship in minimally invasive surgery at The Cleveland Clinic Foundation, in Cleveland, Ohio. He has been named one of the Top Doctors in the state by Connecticut Magazine for three consecutive years.

Dr Casillas specializes in the surgical treatment of a wide range of gastrointestinal problems, including colorectal cancer, colorectal polyps, diverticulitis, rectal prolapse, inflammatory bowel disease, crohn’s disease, ulcerative colitis, anorectal disease, hemorrhoids, fistulas, fissures, and fecal incontinence.

He also performs a wide range of general surgical procedures including gallbladder surgery, hernia, soft tissue masses, breast surgery, and skin lesions. Most of his surgeries are done with the latest minimally invasive techniques including robotic surgery using the Da Vinci robotic system.

Medical School: La Salle University, Mexico City, Mexico
Internship: State University of New York Upstate Medical Center
Residency: State University of New York Upstate Medical Center
Fellowship: The Cleveland Clinic Foundation
Board Certification: Surgery/Colon & Rectal Surgery


Michael M. Deren, MD

Dr. Deren attended college and medical school at Georgetown University. Following graduation he returned to his home state of Connecticut and completed a general surgical residency at Hartford Hospital. His residency was interrupted by military service as a battalion surgeon with the 3rd Marine Division. Following completion of his general surgical residency Dr. Deren went on to a cardiothoracic fellowship at Yale-New Haven Hospital. He has been in surgical practice since then in New London and Norwich, and is board-certified in general and thoracic surgery as well as quality assurance. He has been active in organized medicine locally as President of the New London County Medical Society. He is Past President of the Connecticut State Medical Society (CSMS) and is currently in his 10th year as Chairman of its Board of Trustees. Dr. Deren is a former member of the Governing Council of the AMA/OMSS and is currently a member of the AMA’s Council on Constitution & Bylaws and is the CSMS’s AMA Delegation Chair.

College: Georgetown University
Medical School: Georgetown University
Internship: Hartford Hospital
Residency: Yale-New Haven Hospital
Board Certification: Surgery/Thoracic Surgery

[ No doctors found with name Juan Escalon ]


Mark R. Tousignant, MD

Dr. Tousignant has been a member of the medical staff since 2008 and is board certified in General Surgery.  He completed his training in general surgery at Robert Wood Johnson University Hospital in New Brunswick, NJ.  He attended medical school at MCP-Hahnemann School of Medicine in Philadelphia, PA.  Prior to becoming a surgeon, he was an engineer.

Dr. Tousignant specializes in the treatment of a wide range of general surgery problems with the latest minimally invasive surgery techniques, for the treatment of thyroid disease/cancer, parathyroid disease, hiatal hernia, reflux disease, gallbladder disease, breast surgery, abdominal wall hernia and colorectal disease.  He performs the most laparoscopic inginual and ventral hernias in the area.  Additionally, Dr. Tousignant is one of only a handful of surgeons in the state of Connecticut that performs scarless surgery for the treatment of gallbladder disease.

Moreover, Dr. Tousignant has developed a Bariatric program at Backus, offering laparoscopic adjustable gastric banding procedures.

Medical School: MCP Hahnemann School of Medicine
Internship: Rush University Hospital
Residency: Robert Wood Johnson University Hospital; Middlesex Memorial Hospital, Rush University
Board Certification: Surgery
Professional Interests: Medical Director, Backus Weight Loss Center