J. Mark Barnett, MD

Medical Oncologist / Hematologist

J. Mark Barnett, MD


2030 Mountain View Avenue, Suite 210
Longmont, Colorado 80501


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About J. Mark Barnett, MD

Dr. Mark Barnett is board certified in medical oncology and hematology. He completed his fellowship training at the Brown University program in Providence, Rhode Island. He has practiced in the Longmont community since 2006. He lives in Longmont with his wife and three children and is honored to continue to serve the Longmont community. Dr. Barnett has over 15 years of experience in medical oncology and hematology and has particular interest in the areas of gastrointestinal and genitourinary malignancies. He is an advocate for cancer research, and actively participates in recruiting patients for clinical trials. He has received several awards recognizing his commitment to patient care including the Longmont Physician Service Excellence award. He currently serves on the partnership board for Rocky Mountain Cancer Centers. He actively collaborates with colleagues in a multidisciplinary approach to maximize patient outcomes. He is known throughout the community as a very approachable and compassionate physician.

Board Certifications

Medical Oncology

Clinical Care Expertise

Bladder Cancer
Colorectal Cancer
Gastric Cancer
Gastrointestinal Cancers
Genitourinary malignancies
Esophageal Cancer
Kidney Cancer
Medical Oncology
Pancreatic Cancer
Prostate Cancer



Hematology & Oncology, Brown University School of Medicine, Providence, RI


Internal Medicine, Brown University School of Medicine, Providence, RI

Medical School

Southern Illinois University School of Medicine, Edwardsville, IL

Patient Care Philosophy

I believe in bringing my full attention and focus to each patient at every visit. I believe practicing medicine is an honor that gives us the opportunity to experience the wonderful humanity and resilience of our patients. I learn a great deal from my patients and getting to know each of them personally is the best part of my work.

Additional Information

American Society of Clinical Oncology
Colorado Medical Society
Longmont United Hospital Cancer Committee, Chairman