Reetesh K. Pai, MD
Professor of Pathology

Dr. Pai is a Professor in the Division of Anatomic Pathology, Director of Anatomic Pathology at UPMC Presbyterian, and Director of the Gastrointestinal Pathology Center of Excellence.

Office Location:
Rm. A610
UPMC Presbyterian Hospital
Pathology Department
200 Lothrop Street
Pittsburgh, PA 15213
Contact Information:
Office Telephone: 412-647-3935


  • MD - 2001, University of New Mexico
  • Surgical Pathology and Cytopathology Fellowships, Stanford University

Clinical Expertise

Dr. Pai is a surgical pathologist and cytopathologist with a subspecialty focus in gastrointestinal/pancreatobiliary pathology at the University of Pittsburgh Medical Center, Presbyterian Hospital. His diagnostic expertise includes neoplastic and non-neoplastic diseases of the colon and rectum, appendix, and pancreas.

Research Interests

Dr. Pai's primary research interests are the clinicopathologic and molecular analysis of colorectal and appendiceal neoplasms.

Selected Publications

View Dr. Pai's publications on PubMed

Peer-Reviewed Articles

  • Mills A*, Pai RK, Copland A, Guo F, Pinsky B. A comparison of CMV detection in gastrointestinal mucosal biopsies using immunohistochemistry and PCR performed on formalin-fixed, paraffin-embedded tissue. Am J Surg Pathol 2013; 37:995-1000. (participated in the histological analysis and manuscript preparation)
  • Hartman DJ, Nikiforova MN, Chang DT, Chu E, Bahary N, Brand RE, Zureikat AH, Zeh HJ, Choudry MH, Pingpank JF, Bartlett DL, Pai RK. Signet ring cell colorectal carcinoma: A distinct subset of mucin-poor microsatellite stable signet ring cell carcinoma associated with dismal prognosis. Am J Surg Pathol 2013; 37:969-77.
  • Park WG, Pai RK, Peltz G. Metabolomic-derived novel cyst fluid biomarkers for pancreatic cysts: Glucose and kynurenine. Gastrointest Endoscopy 2013; 78:295-302. (participated in the histological analysis and manuscript preparation)
  • Li C, Zhu Y, Shenoy M, Pai RK, Liu L, Pasricha PJ. Anatomical and functional characterization of a duodeno-pancreatic neural reflex that can induce acute pancreatitis. Am J Physiol Gastrointest Liver Physiol. 2013; 304:G490-500. (participated in the histological analysis and manuscript preparation)
  • Hu H, Chang DT, Nikiforova MN, Kuan SF, Pai RK. Clinicopathologic Features of Synchronous Colorectal Carcinoma: A Distinct Subset Arising From Multiple Sessile Serrated Adenomas and Associated With High Levels of Microsatellite Instability and Favorable Prognosis. Am J Surg Pathol. 2013;37:1660-70.
  • Nikiforova MN, Khalid A, Fasanella KE, McGrath KM, Brand RE, Chennat JS, Slivka A, Zeh HJ, Zureikat AH, Krasinskas AM, Ohori NP, Schoedel KE, Navina S, Mantha GS, Pai RK, Singhi AD. Integration of KRAS testing in the diagnosis of pancreatic cystic lesions: a clinical experience of 618 pancreatic cysts. Mod Pathol. 2013;26:1478-1487. (participated in the histological analysis and manuscript preparation)
  • Hartman DJ, Brand RE, Hu H, Bahary N, Dudley B, Chiosea SI, Nikiforova MN, Pai RK. Lynch syndrome-associated colorectal carcinoma: frequent involvement of the left colon and rectum and late-onset presentation supports a universal screening approach. Hum Pathol. 2013;44:2518-28.
  • Pai RK, Hartman DJ, Gonzalo DH, Lai KK, Downs-Kelly E, Goldblum JR, Liu X, Patil DT, Bennett AE, Plesec TP, Kuan SK, Nikiforova MN, Shadrach B, Pai RK. Serrated lesions of the appendix frequently harbor KRAS mutations and not BRAF mutations indicating a distinctly different serrated neoplastic pathway in the appendix. Hum Pathol. 2014; 45:227-235.
  • Kuan SK, Navina S, Cressman K, Pai RK. Immunohistochemical detection of BRAF V600E mutant protein using the VE1 antibody in colorectal carcinoma is highly concordant with molecular testing but requires rigorous antibody optimization. Hum Pathol. 2014;45:464-72.
  • Singhi AD, Pai RK, Kant JA, Bartholow TL, Zeh HJ, Lee KK, Wijkstrom M, Yadav D, Bottino R, Brand RE, Chennat JS, Lowe ME, Papachristou GI, Slivka A, Whitcomb DC, Humar A. The Histopathology of PRSS1 Hereditary Pancreatitis. Am J Surg Pathol. 2014;38:346-53. (participated in the histological analysis and manuscript preparation)
  • Pai RK, Shadrach BL, Carver P, Heald B, Moline J, Church J, Kalady MF, Burke CA, Plesec TP, Lai KK, Gonzalo DH, Pai RK. Immunohistochemistry for annexin A10 can distinguish sporadic from Lynch syndrome-associated microsatellite unstable colorectal carcinoma. Am J Surg Pathol. 2014;38:518-525.
  • Davison JM, Hartman DA, Singhi AD, Choudry HA, Ahrendt SA, Zureikat AH, Ramalingam L, Nikiforova M, Pai RK. Loss of SMAD4 protein expression is associated with high tumor grade and poor prognosis in disseminated appendiceal mucinous neoplasms. Am J Surg Pathol. 2014 (epub ahead of print).
  • Davison JM, Choudry HA, Pingpank JF, Ahrendt SA, Holtzmann MP, Zureikat AH, Zeh HJ, Ramalingam L, Zhu B, Nikiforova M, Bartlett DL, Pai RK. Clinicopathologic and molecular analysis of disseminated appendiceal mucinous neoplasms: Identification of factors predicting survival and proposed criteria for a three-tiered assessment of tumor grade. Mod Pathol. 2014 (epub ahead of print).
  • Li X, Nadauld L, Ootani A, Corney DC, Pai RK, Gevaert O, Cantrell MA, Rack PG, Neal JT, Chan CWM, Yeung T, Gong X, Yuan J, Wilhelmy J, Robine S, Attardi LD, Plevritis SK, Hung KE, Chen CZ, Ji HP, Kuo CJ. Oncogenic transformation of diverse gastrointestinal tissue in primary organoid culture. Nature Med 2014 (epub ahead of print). (participated in the histological analysis and manuscript preparation)
  • Mojtahed A, Pai RK, Anderson MW, Arber DA, Longacre TA. Reactive lymphoid hyperplasia of the terminal ileum: A benign (lymphoma-like) condition that may harbor aberrant immunohistochemical patterns or clonal immunoglobulin heavy chain gene rearrangements. Applied Immunohistochem Mol Morphol 2014 (epub ahead of print). (participated in the histological analysis and manuscript preparation)
  • Landau MS, Kuan SF, Chiosea S, Pai RK. BRAF-mutated microsatellite stable colorectal carcinoma: An aggressive adenocarcinoma with reduced CDX2 and increased cytokeratin 7 immunohistochemical expression. Hum Pathol 2014 (epub ahead of print).
  • Singhi AD, Davison JM, Choudry HA, Pingpank JF, Ahrendt SA, Holtzman MP, Zureikat AH, Zeh HJ, Ramalingam L, Mantha G, Nikiforova M, Bartlett DL, Pai RK. GNAS is frequently mutated in both low-grade and high-grade disseminated appendiceal mucinous neoplasms but does not affect survival. Hum Pathol 2014 (epub ahead of print).
  • Singhi AD, Nikiforova MN, Fasanella KE, McGrath KM, Pai RK, Ohori NP, Bartholow TL, Brand RE, Chennat JE, Lu X, Papachristou GI, Slivka A, Zeh HJ, Zureikat AH, Lee KK, Tsung A, Mantha GS, Khalid A. Preoperative GNAS and KRAS testing in the diagnosis of pancreatic mucinous cysts. Clin Cancer Res 2014 (epub ahead of print)
  • Hartman DJ, Binion D, Regueiro M, Schraut W, Bahary N, Sun W, Nikiforova M, Pai RK. Isocitrate dehydrogenase-1 is mutated in inflammatory bowel disease-associated intestinal adenocarcinoma with low-grade tubuloglandular histology but not in sporadic intestinal adenocarcinoma. Am J Surg Pathol 2014;38:1147-1156.
  • Mill AM, Liou S, Ford JM, Berek JS, Pai RK, Longacre TA. Lynch syndrome screening should be considered for all patients with newly diagnosed endometrial cancer. Am J Surg Pathol 2014;38:1501-9. (participated in the histological analysis and manuscript preparation)
  • Nadauld LD, Garcia S, Natsoulis G, Bell JM, Miotke L, Hopman ES, Xu H, Pai RK, Palm C, Regan JF, Chen H, Flaherty P, Ootani A, Zhang NR, Ford JM, Kuo CJ, Ji HP. Metastatic tumor evolution and organoid modeling implicate TGFBR2 as a cancer driver in diffuse gastric cancer. Genome Biol 2014;15:428. (participated in the histological analysis and manuscript preparation)
  • Kermanshahi TR*, Jayachandran P, Chang DT, Pai RK. LEF-1 is frequently expressed in colorectal carcinoma and not in other gastrointestinal tract adenocarcinomas: an immunohistochemical survey of 602 gastrointestinal tract neoplasms. Appl Immunohistochem Mol Morphol 2014;22:728-734.
  • Kozak MM, von Eyben R, Pai J, Vossler SR, Limaye M, Jayachandran P, Anderson EM, Shaffer JL, Longacre T, Pai RK, Koong AC, Chang DT. Smad4 inactivation predicts for worse prognosis and response to fluorouracil-based treatment in colorectal cancer. J Clin Pathol. 2015;68:341-5.
  • Ma C, Pai RK. Predictive value of immunohistochemistry in pre-malignant lesions of the gastrointestinal tract. Sem Diagn Pathol 2015. (Epub ahead of print).
  • Dudley B, Brand RE, Thull D, Bahary N, Nikiforova MN, Pai RK. Germline MLH1 mutations are frequently identified in Lynch syndrome patients with colorectal and endometrial carcinoma demonstrating isolated loss of PMS2 immunohistochemical expression. Am J Surg Pathol 2015. (Epub ahead of print).
  • Griffith CC, Pai RK, Schneider F, Duvvuri U, Ferris RL, Johnson JT, Seethala RR. Salivary gland tumor fine-needle aspiration cytology: a proposal for a risk stratification classification. Am J Clin Pathol. 2015 Jun;143(6):839-53.
  • Pollom E, Deng L, Pai RK, Brown JM, Giaccia A, Loo BW, Shultz DB, Le QT, Koong AC, Chang DT. Gastrointestinal toxicities with combined anti-angiogenic and stereotactic body radiation therapy. Int J Radiat Oncol Biol Phys. 2015. (In press)
  • Shah S, Pickham D, Araya H, Kamal A, Pineda C, Shih L, Kong C, Pai RK, Welton M. Prevalence of anal dysplasia and HPV infection in inflammatory bowel disease. Clin Gastroenterol Hepatol 2015. (In press).

Book Chapters

  • Pai RK. Polyps of the Small Intestine. In Surgical Pathology of the GI Tract, Liver, Biliary Tract, and Pancreas, Odze RD, Goldblum JR eds. 2014.
  • Choudry H, Pai RK, Bartlett DL. Appendiceal Tumors. In Textbook of Complex General Surgical Oncology, 2015 (In press).
  • Pai RK. Neoplasms of the Appendix. In Color Atlas and Synopsis: Gastrointestinal Pathology, Xiao SY ed. 2015 (In Press).
  • Landau M and Pai RK. Inflammatory Conditions of the Appendix. In Color Atlas and Synopsis: Gastrointestinal Pathology, Xiao SY ed. 2015 (In Press).