Shannon O'Mahar, MD
Hematology and Oncology

Dr. O'Mahar is a board certified oncologist. She obtained her undergraduate degree from Stanford University and earned her medical degree from the Washington University School of Medicine in St. Louis. She completed her internship at Barnes-Jewish Hospital in St. Louis and her fellowship at the University of Wisconsin - Madison.
Her area of expertise is the treatment of multiple myeloma, myelodysplastic syndromes, monoclonal gammopathy, melanoma and acute and chronic leukemia.
In her free time, Dr. O'Mahar enjoys baking and writing sort stories and poetry.
Her area of expertise is the treatment of multiple myeloma, myelodysplastic syndromes, monoclonal gammopathy, melanoma and acute and chronic leukemia.
In her free time, Dr. O'Mahar enjoys baking and writing sort stories and poetry.
About Me
Specialties
Hematology and Oncology
Gender
Female
Education
Barnes Jewish Hospital/Washington University
Residency, 2008
UW Hospital Graduate Medical Education
Fellowship, 2012
Washington University - St Louis, MO
Internship, 2006
Washington University School of Medicine
Medical School, 2005
Hospital Affiliations
SSM Health St. Mary's Hospital - Janesville
SSM Health St. Mary's Hospital - Madison
Certifications
American Board of IM/Hematology
American Board of IM/Medical Oncology
American Board of Internal Medicine
Drug Enforcement Administration
Wisconsin Medical Examining Board
Medical Interests
Multiple myeloma
Myelodysplastic syndromes
MGUS Monoclonal gammopathy of undetermined significance
Acute lymphoid and myeloid leukemia
Melanoma
Reviews
Rating Breakdown
Reviews are measured on a scale of 1 to 5, with 5 being the best score.
Question Breakdown
4.9Overall Experience5.0Listened Carefully4.9Explained Things Clearly4.9Knew Medical History4.9Involved in Care Decisions4.9Showed Courtesy & Respect
Patient Reviews
SSM Health only displays patient satisfaction data for providers included in our survey process and who have a minimum of 30 returned surveys. The overall rating is an average of all responses to the survey questions listed below. The ratings and comments submitted by patients reflect their own views and opinions. Patient identities are withheld to ensure confidentiality and privacy. Learn more about our survey.
4.9 out of 5
146 ratings,
53 reviews
6/18/2026
She's one of my favorite doctors ever!
6/5/2026
She is the epitome of what is good in cancer care
6/5/2026
I feel very comfortable with her. I was not rushed and confident she knew by history to best address next steps.
5/23/2026
Very knowledgeable and kind
5/22/2026
She doesn’t act like she is better than you.I’m relax when I see her
Map & Directions
SSM Health Cancer Care
1211 Fish Hatchery RoadMadison, WI 53715
Mon
7:00 am - 5:15 pm
Tue
7:00 am - 5:15 pm
Wed
7:00 am - 5:15 pm
Thu
7:00 am - 5:15 pm
Fri
7:00 am - 5:15 pm
Sat
Closed
Sun
Closed



