William J. Chapin, MD, MSCE
Medical Oncology
Accepting new patients
Sees patients age 18 and up
Abramson Cancer Center Perelman 2nd Floor West
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: University of Pennsylvania Health System
  • Fellowship: University of Pennsylvania Health System

What my patients think about me

Average Rating

280 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.

January 2026
attention to detail
December 2025
impressed as competent and knowledge as demonstrated through the time spent exploring background and options
December 2025
he is thorough informative but also makes me feel decision making is collaborative
December 2025
really great bedside matter.

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

Boursi B, Stemmer A, Chapin WJ, Shacham-Shmueli E, Kopetz S, Andre T, Overman MJ, Pietrantonio F, Margalit O. Durable responses to immunotherapy in dMMR/MSI-H metastatic colorectal cancer patients with poor performance status. , American Society of Clinical Oncology Annual Gastrointestinal Meeting, San Francisco, CA. : 2026


Kim RD, Saeed A, Chapin WJ, Kim K, Iyer R, Martin II RC, Grothey A, Gadde S, Feun LG, Gabayan A, Saenger YM, Abdelrahim M, Govada N, Xie B, Cho M, Burgoyne A. A multicenter, open-label study of RP2 oncolytic immunotherapy expressing anti–CTLA-4 in combination with second-line atezolizumab plus bevacizumab in advanced hepatocellular carcinoma (HCC) or in combination with first-line durvalumab in advanced biliary tract cancer (BTC). , American Society of Clinical Oncology Annual Gastrointestinal Meeting, San Francisco, CA.: 2026


Boursi B, Kolkey ZL, Reiss KA, O'Hara MH, Chapin WJ. Comparative effectiveness of oxaliplatin or irinotecan rechallenge vs standard third-line therapies in patients with metastatic colorectal cancer. , American Society of Clinical Oncology Annual Gastrointestinal Meeting, San Francisco, CA. : 2026


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