Rish Pai

Dr. Pai received his BA from Pomona College in Claremont, CA and earned his MD, PhD from Case Western University School of Medicine in Cleveland, Ohio. He completed his anatomic pathology residency at the University of Chicago Medical Center, followed by a gastrointestinal and hepatic pathology fellowship at the same institution. 

Dr. Pai joined Sinai Health System and the University of Toronto in 2025 from the Mayo Clinic in Arizona where he was Professor of Laboratory Medicine and Pathology and Director of the GI/Liver Pathology service.

He is Past-President of the Rodger C. Haggitt Gastrointestinal Pathology Society and has presented nationally and internationally on many aspects of gastrointestinal and hepatic pathology.

Research synopsis

Dr. Pai's research focuses on the histopathology of gastrointestinal cancer with particular emphasis on features that predict prognosis and response to therapy.

Another important aspect of Dr. Pai's work involves developing and validating histological indices for inflammatory diseases of the gastrointestinal tract and liver for use in clinical trials and to better improve patient outcomes in clinical practice.

Selected publications

Pai RK, Eslinger C, Lee K, Farchoukh LF, Walden D, Emiloju O, Storandt M, Hagen CE, Pfeiffer A, Sonbol MB, Ahn D, Bekaii-Saab T, Ness A, Hubbard J, Wu C, Westerling-Bui T, Bao R, Ou FS, Pai RK. Quantitative Analysis of Rectal Cancer Biopsies With the Digital Pathology Segmentation Algorithm QuantCRC Associates With Therapy Response and Recurrence. Lab Invest. 2025 Apr 29;105(8):104187

Wu C, Pai RK, Kosiorek H, Banerjee I, Pfeiffer A, Hagen CE, Hartley CP, Graham RP, Sonbol MB, Bekaii-Saab T, Xie H, Sinicrope FA, Patel B, Westerling-Bui T, Shivji S, Conner J, Swallow C, Savage P, Cyr DP, Kirsch R, Pai RK. Improved Risk-Stratification Scheme for Mismatch-Repair Proficient Stage II Colorectal Cancers Using the Digital Pathology Biomarker QuantCRC. Clin Cancer Res. 2024 May 1; 30 (9):1811-1821 

Pai RK, D'Haens G, Kobayashi T, Sands BE, Travis S, Jairath V, De Hertogh G, Park B, McGinnis K, Redondo I, Lipitz NG, Gibble TH, Magro F. Histologic assessments in ulcerative colitis: the evidence behind a new endpoint in clinical trials. Expert Rev Gastroenterol Hepatol. 2024 Jan-Feb; 18 (1-3):73-87 

Lebwohl B, Ma C, Lagana SM, Pai RK, Baker KA, Zayadi A, Hogan M, Bouma G, Cellier C, Goldsmith JD, Lundin KEA, Pinto-Sanchez MI, Robert ME, Rubio-Tapia A, Sanders DS, Schaeffer DF, Semrad CE, Silvester JA, Verdu EF, Verma R, Wu TT, Feagan BG, Crowley E, Jairath V, Murray JA. Standardizing Randomized Controlled Trials in Celiac Disease: An International Multidisciplinary Appropriateness Study. Gastroenterology. 2024 Jan; 166 (1):88-102 

Magro F, Pai RK, Kobayashi T, Jairath V, Rieder F, Redondo I, Lissoos T, Morris N, Shan M, Park M, Peyrin-Biroulet L. Resolving Histological Inflammation in Ulcerative Colitis With Mirikizumab in the LUCENT Induction and Maintenance Trial Programmes. J Crohns Colitis. 2023 Oct 20; 17 (9):1457-1470 

Pai RK, Banerjee I, Shivji S, Jain S, Hartman D, Buchanan DD, Jenkins MA, Schaeffer DF, Rosty C, Como J, Phipps AI, Newcomb PA, Burnett-Hartman AN, Le Marchand L, Samadder NJ, Patel B, Swallow C, Lindor NM, Gallinger SJ, Grant RC, Westerling-Bui T, Conner J, Cyr DP, Kirsch R, Pai RK. Quantitative Pathologic Analysis of Digitized Images of Colorectal Carcinoma Improves Prediction of Recurrence-Free Survival. Gastroenterology. 2022 Dec; 163 (6):1531-1546.

Pai RK, Jairath V, Hogan M, Zou G, Adeyi OA, Anstee QM, Aqel BA, Behling C, Carey EJ, Clouston AD, Corey K, Feagan BG, Kleiner DE, Ma C, McFarlane SC, Noureddin M, Ratziu V, Valasek MA, Younossi ZM, Harrison SA, Loomba R. Reliability of histologic assessment for NAFLD and development of an expanded NAFLD activity score. Hepatology. 2022 Oct; 76 (4):1150-1163 

Ma C, Sedano R, Almradi A, Vande Casteele N, Parker CE, Guizzetti L, Schaeffer DF, Riddell RH, Pai RK, Battat R, Sands BE, Rosty C, Dubinsky MC, Rieder F, Harpaz N, Abreu MT, Bryant RV, Lauwers GY, Kirsch R, Valasek MA, Crowley E, Sandborn WJ, Feagan BG, Pai RK, Jairath V. An International Consensus to Standardize Integration of Histopathology in Ulcerative Colitis Clinical Trials. Gastroenterology. 2021 Jun; 160 (7):2291-2302 

Almradi A, Ma C, D'Haens GR, Sandborn WJ, Parker CE, Guizzetti L, Borralho Nunes P, De Hertogh G, Feakins RM, Khanna R, Lauwers GY, Mookhoek A, Pai RK, Peyrin-Biroulet L, Riddell R, Rosty C, Schaeffer DF, Valasek MA, Singh S, Crowley E, Feagan BG, Jairath V, Pai RK. An expert consensus to standardise the assessment of histological disease activity in Crohn's disease clinical trials. Aliment Pharmacol Ther. 2021 Apr; 53 (7):784-793 

Pai RK, Hartman DJ, Leighton JA, Pasha SF, Rivers CR, Regueiro M, Binion DG, Pai RK. Validated Indices for Histopathologic Activity Predict Development of Colorectal Neoplasia in Ulcerative Colitis. J Crohns Colitis. 2021 Sep 25; 15 (9):1481-1490 

Pai RK, Hartman DJ, Rivers CR, Regueiro M, Schwartz M, Binion DG, Pai RK. Complete Resolution of Mucosal Neutrophils Associates With Improved Long-Term Clinical Outcomes of Patients With Ulcerative Colitis. Clin Gastroenterol Hepatol. 2020 Oct; 18 (11):2510-2517

Jairath V, Peyrin-Biroulet L, Zou G, Mosli M, Vande Casteele N, Pai RK, Valasek MA, Marchal-Bressenot A, Stitt LW, Shackelton LM, Khanna R, D'Haens GR, Sandborn WJ, Olson A, Feagan BG, Pai RK. Responsiveness of histological disease activity indices in ulcerative colitis: a post hoc analysis using data from the TOUCHSTONE randomised controlled trial. Gut. 2019 Jul; 68 (7):1162-1168

Honours and awards

President, Rodger C. Haggitt Gastrointestinal Pathology Society (2020-2021)

Jack Yardley Investigator Award from the Rodger C. Haggitt Gastrointestinal Pathology Society (2019)