William J. Chapin, MD, MSCE
Medical Oncology
Accepting new patients
Sees patients age 18 and up
Abramson Cancer Center Perelman 2nd Floor West
Make an appointmentCall 215-615-5858
Penn Medicine Provider

About me

  • Assistant Professor of Medicine (Hematology-Oncology) at the Hospital of the University of Pennsylvania

Education and training

  • Medical School: University of Chicago
  • Residency: Hospital of the University of Pennsylvania
  • Fellowship: Hospital of the University of Pennsylvania

What my patients think about me

Average Rating

264 reviews

Comments are submitted by patients and reflect their views and opinions. The comments are not endorsed by and do not necessarily reflect the views of Penn Medicine.

November 2025
he's excellent doctor
October 2025
good service
October 2025
dr. chapin is thorough with his explanations, does not rush us as we try to understand all that is being provided for emanuel. he is very personable and takes his time to insure all of our questions are answered
September 2025
gave options, confirmed with my other doctors before seeing me

Insurance accepted

My Locations

Penn Medicine hospital privileges

  • Hospital of the University of Pennsylvania: Has privileges to treat patients in the hospital.
Dr. Chapin is a Penn Medicine physician.

Qualifications and experience

Treatments and Conditions

My research

Lin JK, Niu J, Giordano SH, Li P, Snyder RA, Liao K, Li M, Aparicio A, Chapin W, Zhang J, Xiang J, Perera N, Pain D, Guerra CE, Doshi JA. Racial and Ethnic Disparities Along the Treatment Cascade Among Medicare Fee-for-Service Beneficiaries With Metastatic Breast, Colorectal, Lung, and Prostate Cancers , J Clin Oncol: 2025

Swami N, Hwang WT, Mamtani R, O'Hara MH, Chapin WJ. Second-Line Treatment Strategies for Right-Sided, RAS/RAF Wild-Type Colorectal Cancer , JAMA Netw Open, 8: 2025,e2515087

Swami N, Hwang WT, O’Hara MH, Chapin WJ. Real-world evaluation of a “hyperselection” predictive biomarker for anti-EGFR therapy benefit in patients with RAS/RAF wild-type, MMRp/MSS mCRC , J Clin Oncol, 43(16): 2025

Nishwant Swami, Wei-Ting Hwang, Ronac Mamtani, Mark O'Hara, William Chapin Real-world survival comparison of second-line treatment strategies for patients with RAS/RAF wild-type, right-sided metastatic colorectal cancer. , Journal of Clinical Oncology, 43(4_suppl): 2025,73

Margalit O, Stemmer A, Chapin WJ, Schacham-Shmueli E, Kopetz S, Andre T, Overman MJ, Pietrantonio F, Boursi B Duration of Immunotherapy in dMMR/MSI-H Metastatic Colorectal Cancer Patients , European Journal of Cancer, 212: 2024,114336

Chapin WJ, Hwang W, Mamtani R, O’Hara MH Real-world uptake and effectiveness of triplet versus doublet chemotherapy with bevacizumab in patients with metastatic colorectal cancer in the United States , ESMO Gastrointestinal Oncology, 5: 2024,100087

Chapin WJ, Hwang W, Mamtani R, O’Hara MH Low- vs High-Dose 5-FU in Triplet Chemotherapy Plus Bevacizumab for Patients With Colorectal Cancer , JAMA Netw Open, 7(7): 2024,e2424855

Rathore S, Reiss KA, Teitelbaum UR, Chapin WJ Exploring the association of smoking status with clinical outcomes in patients with mPDAC treated on a clinical trial of maintenance niraparib plus immune checkpoint blockade. , American Society of Clinical Oncology Annual Meeting, Chicago, IL. , 42(suppl 16): 2024,Abstract e16302

William Joseph Chapin, Wei-Ting Hwang, Ronac Mamtani, and Mark H. O'Hara Real-world comparison of low- versus high-dose continuous 5FU infusion in patients receiving triplet chemotherapy plus bevacizumab for newly diagnosed metastatic colorectal cancer (mCRC). , Journal of Clinical Oncology , 42(3_suppl): 2024,62-62

William Joseph Chapin, Wei-Ting Hwang, Ronac Mamtani, Mark H O'Hara Real-world comparison of triplet-versus doublet-chemotherapy with bevacizumab in patients with newly diagnosed metastatic colorectal cancer (mCRC). , The American Society of Clinical Oncology Annual meeting, Chicago, IL., 41(16_suppl): 2023,3574-3574