Colorectal Surgery
About Us
Dr. Andrew Shelton is the Chief of Colorectal Surgery at Stanford University, and leads a group of experienced board-certified colorectal surgeons (Drs. Dawes, Gahagan, Gurland, Kin, Kirilcuk, Morris, and Shelton) who treat diagnoses including: colorectal cancer, inflammatory bowel disease, diverticular disease, polyposis syndromes, anorectal disorders, and pelvic floor dysfunction such as rectal prolapse and fecal incontinence.
The group has advanced surgical expertise in total mesorectal excision for rectal cancer; minimally invasive surgical techniques including laparoscopy, robotic surgery, and transanal endoscopic microsurgery; ileal pouches for ulcerative colitis or familial adenomatous polyposis; care of the complex Crohn's patient, sphincter-preserving operations for low rectal cancers; and cutting edge approaches to rectal prolapse and fecal incontinence.
Our colorectal surgeons actively collaborate with gastroenterologists, medical oncologists, radiation oncologists, and surgeons from other sub-specialties to offer patients an integrated and individualized treatment plan. Patients with inflammatory bowel disease (Crohn’s disease or ulcerative colitis) can be seen in our new Multidisciplinary IBD Program where colorectal surgeons and gastroenterologists offer joint visits and direct input from dieticians, pharmacist, radiologist, social workers, and mental health professionals.
The section of Colorectal Surgery leads clinical, informatics, and health services research and actively collaborates in lab-based translational efforts across departments.
Colorectal Surgeons








Our Advanced Practice Providers
Kelsey Ayers, PA-C
Kelsey Ayers is a physician assistant specializing in colorectal surgery. Her primary focus includes acute care management of postoperative and hospitalized patients. She completed her graduate training at Stanford University in 2020. She previously worked in reproductive health before joining Stanford Health Care in 2022. She is still involved with the physician assistant program at Stanford as a clinical preceptor.
- Professional Education: Stanford Primary Care Associate Program, 2020
Allan Kalaw, NP
- Professional Education: United States University (2016) CA
- Board Certification: American Academy of Nurse Practitioners, Nurse Practitioner (2017)
Margaret (Meg) Folk-Tolbert, NP
Meg Tolbert is a Nurse Practitioner with colorectal surgery at Stanford Hospital. She earned her undergraduate and graduate degrees from Villanova University. She has been adjunct at the PA School at Stanford University.
- Board Certification: American Nurses Credentialing Center, Nurse Practitioner (1998)
- Professional Education: Villanova University (1997) PA
- Professional Education: Villanova University (1984) PA
Tricia Marcos, NP
Tricia Marcos is a nurse practitioner at Stanford Health Care who specializes in gastrointestinal (GI) oncology.
- Board Certification: American Nurses Credentialing Center, Nurse Practitioner (2018)
- Professional Education: UCSF School Of Nursing (2018) CA
Make an Appointment
Gastointestinal (GI) Cancer Program in Emeryville
5800 Hollis Street
Emeryville, CA 94608
Tel: (833) 444-7622
Gastointestinal (GI) Cancer Program in Palo Alto
875 Blake Wilbur Drive
Palo Alto, CA 94304
Tel: (650) 498-6000
Pelvic Health Center
450 Broadway Street
Pavilion D, 2nd Floor
Redwood City CA, 64063
Tel: (650) 721-2700
Gastrointestinal (GI) Cancer Program in Pleasanton
5725 W. Las Positas Blvd. Suite 100
Pleasanton, California 94588
925-734-8130