Medical Director

Thomas D. Horn, MD

Thomas Horn, MD is the medical director of MGPO Dermatopathology Associates, Clinical Professor of Dermatology and Pathology, Harvard Medical School and practices clinical dermatology at Massachusetts General Hospital.  He is board-certified in dermatology and dermatopathology.

Previously, he served as head of the Division of Dermatopathology at the Johns Hopkins Hospital and is the former chair of Dermatology for the University of Arkansas for Medical Sciences.

Throughout his career, Dr. Horn has provided services as a dermatopathologist. He possesses expertise in the microscopic evaluation of the full spectrum of skin disorders. While at Johns  Hopkins, he established himself as an authority in the histologic diagnosis of cutaneous graft-vs-host disease and he continues to receive cases from around the world.

Professionally, he served as Secretary-Treasurer and President of The American Society of Dermatopathology.  He has lectured extensively; published nearly 100 journal publications; and co-authored textbooks such as the Primer of Dermatopathology, Dermatopathology in Systematic Diseases, and Dermatology.

Dr. Horn is recognized both nationally and internationally as an expert in his field.  His particular interests are in inflammatory conditions of the skin, especially clinical-pathologic correlation.


Our Doctors

Timothy quinn

Timothy R. Quinn, MD, CM is board certified in Dermatopathology and Anatomic Pathology and is an Instructor at Harvard Medical School.

Prior to joining MGPO Dermatopathology Associates, Dr. Quinn was the director of Dermpath Diagnostics, New England. He was a founding member and Medical Director of DermDX Boston, and an associate Dermatopathologist at Pathology Services in Cambridge, Massachusetts. He has over 20 years of experience in the diagnosis of complex skin diseases and cancers. He is licensed and certified by the American Board of Pathology in Anatomic Pathology and the American Board of Pathology and Dermatology with special qualification in Dermatopathology.

Dr. Quinn is an honors graduate from the McGill University Faculty of Medicine in Montreal, Quebec, Canada. Following an internship in comprehensive surgery at the Toronto General Hospital, Dr. Quinn completed a residency in anatomic pathology and a fellowship in dermatopathology at the Harvard Medical School/Massachusetts General Hospital, where he studied with several distinguished dermatopathologists including the late Dr. Wallace Clark, Jr. and Dr. Martin C. Mihm, Jr. He earned an Honors Bachelor of Science Degree in Biochemistry from McMaster University, Hamilton, Ontario, Canada, and was a Rotary Foundation Scholar at University College Cork, Republic of Ireland.

Dr. Quinn is a member of the College of American Pathologists, the American Society of Dermatopathology, the New England Dermatological Society, the Massachusetts Academy of Dermatology, and the Maine Dermatology Society. He currently teaches at the Harvard Medical School, and received the Department of Dermatology Award for Excellence in Teaching 2008.

Dr. Quinn’s areas of interests include melanocytic and soft tissue neoplasia, panniculitis, and inflammatory dermatoses of the gynecological/urogenital tracts. He has published extensively in leading dermatopathology journals and has authored several chapters in academic medical textbooks.


Mariko Yasuda, MD

Mariko Ruth Yasuda, MD is a board certified dermatologist, dermatopathologist and Instructor in Dermatology at Harvard Medical School. Dr. Yasuda completed her internship in Internal Medicine, her residency in dermatology, and a fellowship in dermatopathology at the University of Massachusetts Medical School in Worcester, Massachusetts. While at UMass, Dr. Yasuda was awarded Intern of the Year for her clinical knowledge, empathy, and compassion and later served as chief resident during her dermatology residency. She received her medical degree from Albany Medical College in Albany, New York where she was inducted into the Alpha Omega Alpha Honor Society. As a graduate of Wellesley College, she obtained her bachelor's degree in piano performance.

Dr. Yasuda has presented several posters at the American Academy of Dermatology as well as The American Society of Dermatopathology and has published articles in the Journal of the American Academy of Dermatology and the Journals of Clinical and Experimental Dermatology. She also enjoys participating in resident education, teaching dermatology and dermatopathology.

Dr. Yasuda is interested in the interpretation of skin biopsies and its influence on the diagnosis and management of cutaneous disease. In addition to general dermatology, her clinical interests include hair loss, pediatric dermatology, melanoma, bullous disorders, psoriasis, acne, and drug-induced rashes.


William Lin, MD

William M. Lin, MD is a board-certified dermatologist and dermatopathologist. He is an Instructor in Dermatology at Harvard Medical School.

Dr. Lin earned his bachelor’s and master’s degrees in Chemistry and Chemical Biology at Harvard College and Harvard Graduate School of Arts and Sciences, concentrating on cancer drug discovery. He received his medical degree from Yale School of Medicine and completed his internship in Internal Medicine at Massachusetts General Hospital. He is a graduate of the Harvard Combined Dermatology Residency program where he served as Chief Resident. He subsequently completed fellowship training in the Harvard Dermatopathology Fellowship Program.

Dr. Lin is interested in clinicopathologic correlation and cares for patients with general dermatologic disorders and skin cancers. His clinical and research focus centers around the pathogenesis, diagnosis and treatment of melanoma and other skin cancers. His work has been recognized by awards and grants from the Dermatology Foundation, American Skin Association, Society of Investigative Dermatology, and Affymetrix, Inc., and he has published in Nature, Nature Genetics, Journal of Investigative Dermatology and the Journal of the American Academy of Dermatology. He is a contributing author to the Dermatology section of the Pocket: Primary Care handbook for clinicians and currently serves as the Section Editor for Pigmented Lesions and Melanoma at Visual Dx, Inc.

Dr. Lin's clinical interests are: acne and rosacea, atopic dermatitis (eczema), basal cell carcinoma, cutaneous reactions to chemotherapeutic agents, general dermatology, melanoma, nevi (moles), psoriasis, skin cancer, and squamous cell carcinoma.


Lyn Duncan

Lyn McDivitt Duncan, MD is the Director of the MGH Dermatopathology Service, and has been a full time dermatopathologist at the MGH for over 25 years.  

Professionally, she serves on the Executive Committee and the Board of Directors of the American Society of Dermatopathology, served as Program Director of the Harvard Dermatopathology Training Program from 1993-2003, and in 1995 she developed the Harvard Dermatopathology Update CME course which continues to attract participants worldwide. Dr. Duncan is a Professor at Harvard Medical School and serves on the Advisory Board of the Harvard/MIT Health Sciences & Technology Program.

Dr. Duncan is recognized nationally and internationally as an expert dermatopathologist.  Her expertise covers all diseases of the skin.  In addition to daily routine signout, her consultative practice focuses on cutaneous oncology, particularly melanoma and lymphoma.  She has published over 100 scholarly articles and important case reports including many Case Records published in the New England Journal of Medicine.  She has edited numerous textbooks including most recently the Atlas of Essential Dermatopathology and the Atlas of Cutaneous Lymphoma. Dr. Duncan has also contributed to International Consensus documents including the WHO Blue Books.  She is an active member of key international multidisciplinary groups that meet annually to address important issues in diagnosis and patient management in skin cancer.  Her particular interests are in cutaneous oncology and distinguishing benign mimics from malignant tumors.

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