Leo Mascarenhas

Leo Mascarenhas

Pediatric Hematologist, Pediatric Oncologist

Sarcoma

Cedars-Sinai Medical Center

Location USA, Los Angeles

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Dr. Leo Mascarenhas is a pediatric hematologist-oncologist and internationally recognized leader in the clinical research and treatment of pediatric sarcomas and rare childhood cancers. He currently serves as Professor of Pediatrics and Medicine, Director of the Division of Pediatric Hematology/Oncology, and Medical Director of the Adult and Pediatric Sarcoma Program at Cedars-Sinai Medical Center and Guerin Children’s in Los Angeles, California. With more than 25 years of clinical and research experience, Dr. Mascarenhas has been a principal investigator and study chair on landmark Children’s Oncology Group (COG) and multi-institutional clinical trials for Ewing sarcoma, rhabdomyosarcoma, osteosarcoma, and other rare pediatric solid tumors. He is one of the leading figures in the development of TRK inhibitor therapy for pediatric TRK fusion cancers, including larotrectinib, and has contributed seminal work in liquid biopsy, molecular diagnostics, and developmental therapeutics for children with sarcomas and vascular anomalies.

Current Positions

  • Professor, Department of Pediatrics, Cedars-Sinai Medical Center, July 2025–present
  • Professor, Department of Medicine, Cedars-Sinai Medical Center, July 2025–present
  • Director, Division of Pediatric Hematology/Oncology, Cedars-Sinai Medical Center, January 2024–present
  • Medical Director, Adult and Pediatric Sarcoma Program, Cedars-Sinai Cancer Institute, January 2024–present
  • Staff Physician, Guerin Children’s, Cedars-Sinai Medical Center, January 2024–present
  • Staff Physician, Department of Medicine, Cedars-Sinai Medical Center, January 2024–present

Education

  • Pre-University Certificate (BA equivalent), St. Joseph’s College of Arts and Science, Bangalore, India, 1984
  • MBBS, St. John’s Medical College, Bangalore, India, 1989
  • MS, University of Southern California, Los Angeles, 2008

Postgraduate Training

  • General Rotating Internship, St. John’s Medical College, India, 1989–1990
  • Residency, Pediatrics, New York Medical College, Valhalla, New York, 1992–1995
  • Clinical Fellowship, Pediatric Hematology/Oncology, Children’s Hospital Los Angeles, 1995–1998
  • Clinical Fellowship, Research Immunology/Bone Marrow Transplantation, Children’s Hospital Los Angeles, 1998–1999

Board Certifications

  • Pediatrics, American Academy of Pediatrics, 1995
  • Pediatric Hematology/Oncology, American Academy of Pediatrics, 1998

Professional Experience

  • General Physician, St. Ignatius Hospital, India, 1990
  • General Physician, Emmaus Swiss Referral Hospital, 1990–1992
  • Tutor, Department of Physiology, St. John’s Medical College, Bangalore, India, 1992
  • Instructor of Pediatrics, University of California, Los Angeles (UCLA), 1999–2001
  • Assistant Professor of Clinical Pediatrics, UCLA, 2001–2007
  • Attending Physician, Children’s Hospital Los Angeles (CHLA), Department of Pediatrics, July 1998–December 2023
  • Associate Director, Bone and Soft Tissue Tumor Program, CHLA, 1998–2011
  • Director, Clinical Trials Office, Cancer and Blood Diseases Institute, CHLA, 2008–2019
  • Associate Professor of Clinical Pediatrics, Keck School of Medicine, University of Southern California, 2007–2023
  • Division Head, Oncology, Cancer and Blood Diseases Institute, CHLA, 2011–2013
  • Director, Sarcoma and Solid Tumor Program, Cancer and Blood Diseases Institute, CHLA, 2011–2023
  • Section Head, Oncology, Cancer and Blood Diseases Institute, CHLA, 2013–2023
  • Deputy Director, Cancer and Blood Diseases Institute, CHLA, 2013–2023
  • Associates Sarcoma Program Chair (Endowed), Cancer and Blood Diseases Institute, CHLA, 2016–2023
  • Acting Professor, Departments of Pediatrics and Medicine, Cedars-Sinai Medical Center, 2024–June 2025
  • Professor and Director, Division of Pediatric Hematology/Oncology, Cedars-Sinai Medical Center, July 2025–present

Research Activity

  • Ewing sarcoma: One of the leading COG investigators in Ewing sarcoma clinical trials; study chair or co-investigator on multiple phase II/III trials including AEWS1031 and studies evaluating interval-compressed chemotherapy, local control strategies, molecular prognostication, and second malignant neoplasms; principal contributor to trabectedin and low-dose irinotecan trials targeting EWS::FLI1 (SARC037, Nature Medicine 2026)
  • Rhabdomyosarcoma: Extensive clinical trial leadership in rhabdomyosarcoma (RMS), including ARST0921, ARST2031 (vinorelbine and maintenance therapy), and international INSTRuCT pooled analyses; research on alveolar versus embryonal RMS treatment responses, adolescent and young adult RMS outcomes, and TRK fusion RMS
  • TRK inhibitor therapy (larotrectinib): Key investigator in the SCOUT trial and multiple analyses of larotrectinib in pediatric TRK fusion sarcomas and mesenchymal tumors; co-author on landmark publications in Journal of Clinical Oncology on elective discontinuation and long-term safety and efficacy
  • Osteosarcoma: Principal investigator on SARC038 (regorafenib plus nivolumab) and gemcitabine/nab-paclitaxel phase II studies; research on pulmonary metastasectomy outcomes and liquid biopsy surveillance
  • Liquid biopsy and circulating tumor DNA: Co-investigator on LBSEQ4KIDS, developing low-pass whole genome sequencing (LP-WGS) and pediatric-specific targeted cell-free DNA sequencing assays for diagnosis and disease monitoring of pediatric solid tumors; published landmark results in NPJ Precision Oncology (2023)
  • Hepatoblastoma and liver tumors: Research on molecular characterization, histopathology, and prognosis in hepatoblastoma; contributor to Children’s Hepatic Tumors International Collaboration analyses (JAMA Network Open, 2022)
  • Vascular anomalies: Active clinical and research program in vascular anomalies including kaposiform hemangioendothelioma and lymphatic anomalies
  • Developmental therapeutics: Principal investigator on phase I and II trials across multiple drug classes for pediatric solid tumors including immune checkpoint inhibitors, ADCs (mecbotamab vedotin/AXL-targeting), TRK inhibitors, and novel combinations; COG Voting Body Chair

Grants and Funded Research (Select)

  • Principal Investigator, Evaluation of Safety and Efficacy of PEEL-224 as a Single Agent and with Vincristine and Temozolomide in Children, Adolescents, and Young Adults with Solid Tumors (Phase One Foundation), May 2026
  • Principal Investigator, COG Research Foundation NCTN Network Group Operations Center, March 2026–February 2031
  • Co-Investigator, Phase 1/2 Study of Cobolimab in Combination with Dostarlimab in Pediatric and Young Adult Participants with Newly Diagnosed and Relapsed/Refractory Tumors (GSK), February 2025
  • Principal Investigator, Comparing Functional and Quality of Life Outcomes after Selumetinib vs Carboplatin Vincristine in Children with Newly Diagnosed Low Grade Glioma (Public Health Institute), January 2024–December 2028
  • Principal Investigator, The LIFFT Study: Lurbinectedin in FET Fusion Tumors (Children’s Hospital of Philadelphia), July 2023–November 2026
  • Co-PI, A Phase 2 Study of Regorafenib in Combination with Nivolumab in Patients with Refractory or Recurrent Osteosarcoma (Gateway for Cancer Research/Phase One Foundation), January 2021–December 2024
  • Principal Investigator, Early Phase Clinical Trials Program (Names Family Foundation), January 2017–December 2025
  • Principal Investigator, Lymphatic Anomalies Registry (Boston Children’s Hospital), 2018–2023
  • Principal Investigator, Bone and Soft Tissue Tumor Project (Linda Tallen and David Paul Kane Foundation), 2011–2020
  • Principal Investigator, COG NCTN Network Group Operations Center Voting Body Chair (Public Health Institute / NIH/NCI), 2024–present

Honors and Awards

  • Los Angeles Magazine’s Top Doctors, 2017–2025 (multiple years)
  • Pasadena Magazine’s Top Doctors, 2008–2024 (multiple years)
  • Southern California Super Doctors, 2010–2024 (multiple years)
  • Top Reviewed Pediatric Hematologist-Oncologist, 2023
  • Best Doctors in America, 2007–2020 (multiple years)
  • Top Doctors, Castle Connolly Ltd., 2018–2020
  • Walter Laug Distinguished Teaching Award for Inspirational Teaching and Guidance, Pediatric Hematology Oncology Fellowship, Children’s Hospital Los Angeles, 2009
  • Philip E. Rothman Memorial Award for Outstanding Teaching, Guidance and Inspiration, Children’s Hospital Los Angeles, 2006
  • 8th Junior Faculty Mentored Career Development Award, Children’s Hospital Los Angeles, 2005
  • Scholarship Award for Clinical Oncologists in Molecular Biology, American Association for Cancer Research, 1997
  • Bristol Myers Squibb Award for Superior Academic Achievement, New York Medical College, 1995
  • Travel Merit Award, American Society of Hematology, 1999
  • First Rank in Obstetrics and Gynecology, St. John’s Medical College, 1989
  • Most Talented Student Award, St. John’s Medical College, 1988
  • Certificates of Honor in Pathology, Anatomy; Certificates of Merit in Pharmacology and Microbiology, St. John’s Medical College, 1986–1987

Memberships / Affiliations

  • American Society of Clinical Oncology (ASCO), 2002–present
  • American Society of Pediatric Hematology/Oncology (ASPHO), 1999–present
  • International Society of Pediatric Oncology (SIOP), 1999–present
  • American Association for Cancer Research (AACR), 1996–present
  • Connective Tissue Oncology Society (CTOS), 2010–present
  • American Pediatric Society, 2019–present
  • International Society for the Study of Vascular Anomalies, 2023–present
  • Children’s Oncology Group (COG) — Voting Body, Voting Body Steering Committee, Executive Committee
  • European Pediatric Soft Tissue Sarcoma Study Group (EpSSG)
  • Society for Pediatric Research
  • Editorial Service: Journal of Clinical Oncology, Clinical Cancer Research, Annals of Oncology, JAMA Oncology, European Journal of Cancer, Pediatric Blood and Cancer, Journal of
  • Pediatric Hematology and Oncology, Cancer, Cancer Reports, Journal of Adolescent and Young Adult Oncology, Faculty Reviews, PLOS Medicine, American Journal of Clinical Oncology

Areas of Specialization

  • Pediatric sarcomas: Ewing sarcoma, rhabdomyosarcoma, osteosarcoma, soft tissue sarcomas
  • Adult and pediatric sarcoma program leadership
  • TRK fusion cancer and targeted therapy (larotrectinib)
  • Developmental therapeutics and phase I/II clinical trials
  • Rare pediatric solid tumors and hepatoblastoma
  • Liquid biopsy and circulating tumor DNA in pediatric oncology
  • Vascular anomalies
  • Pediatric hematologic malignancies
  • Clinical trials design, leadership, and infrastructure
  • Adolescent and young adult oncology

Publications

Dr. Mascarenhas has authored and co-authored more than 329 publications, including landmark original research articles, clinical trial reports, review articles, and book chapters in journals including Nature Medicine, Journal of Clinical Oncology, JAMA Network Open, NPJ Precision Oncology, Science Translational Medicine, Annals of Oncology, Pediatric Blood & Cancer, Clinical Cancer Research, European Journal of Cancer, and Hematology/Oncology Clinics of North America.

Select Recent Publications:

Grohar PJ, Heise R, Wedekind MF, Mascarenhas L, et al. “Trabectedin and low-dose irinotecan to target EWS::FLI1 in Ewing sarcoma: a phase 1/2 trial.” Nature Medicine, April 2026.

Gillani R, Shulman DS, DelRocco NJ, Mascarenhas L, et al. “Molecular Characterization Informs Prognosis in Patients With Localized Ewing Sarcoma: A Report From the Children’s Oncology Group.” Journal of Clinical Oncology 43(35):3750–3759, December 2025.

Mascarenhas L, Albert CM, Orbach D, et al. “Larotrectinib Safety and Efficacy in Patients with TRK Fusion Sarcomas and Prolonged Response.” ESMO Rare Cancers 4:100043, December 2025.

Ahmed SK, Binitie O, Krailo M, Mascarenhas L, et al. “Factors Associated With Primary Site Local Therapy in Patients With Nonmetastatic Ewing Sarcoma Treated With Interval-Compressed Chemotherapy.” International Journal of Radiation Oncology, Biology, Physics, November 2025.

Mercolini F, Sparber-Sauer M, Mascarenhas L, et al. “Single site metastatic rhabdomyosarcoma: An INSTRuCT pooled analysis.” European Journal of Cancer 229:115793, October 2025.

Weiss AR, Ferrari A, Mascarenhas L, et al. “Current Approaches to the Treatment of Pediatric Soft Tissue Sarcomas: Rhabdomyosarcoma and Nonrhabdomyosarcoma Soft Tissue Sarcomas.” Hematology/Oncology Clinics of North America 39(4):727–748, August 2025.

Indelicato DJ, Callan AK, Ahmed SK, Mascarenhas L, et al. “Preoperative Radiotherapy in Patients With Localized Ewing Sarcoma Enrolled on AEWS1031.” Pediatric Blood & Cancer 72(8):e31820, August 2025.

Mascarenhas L, DuBois SG, Albert CM, et al. “Elective Discontinuation of Larotrectinib in Pediatric Patients With TRK Fusion Sarcomas and Related Mesenchymal Tumors.” Journal of Clinical Oncology 43(10):1180–1187, April 2025.

DuBois SG, Mascarenhas L. “Ewing Sarcoma.” In: Rudolph’s Pediatrics, 24th Edition. McGraw Hill Professional, January 2026.

Akshintala S, Sundby RT, Bernstein D, Mascarenhas L, et al. “Phase I trial of Ganitumab plus Dasatinib to Cotarget IGF1R and Src Family Kinase YES in Rhabdomyosarcoma.” Clinical Cancer Research 29(17):3329–3339, September 2023.

Christodoulou E, Yellapantula V, O’Halloran K, Mascarenhas L, et al. “Combined low-pass whole genome and targeted sequencing in liquid biopsies for pediatric solid tumors.” NPJ Precision Oncology 7(1):21, February 2023.

Zhou S, Malvar J, Chi Y-Y, Mascarenhas L, et al. “Independent Assessment of the Children’s Hepatic Tumors International Collaboration Risk Stratification for Hepatoblastoma.” JAMA Network Open 5(2):e2148013, February 2022.

Crane JN, Xue W, Qumseya A, Mascarenhas L, et al. “Clinical group and modified TNM stage for rhabdomyosarcoma: A review from the Children’s Oncology Group.” Pediatric Blood & Cancer 69(6):e29644, June 2022.

Kuo C, Warren M, Malvar J, Mascarenhas L, et al. “Kaposiform hemangioendothelioma of the bone in children and adolescents.” Pediatric Blood & Cancer 69(1):e29392, January 2022.