Histiocytic proliferations.

The study of Histiocytic lesions has been a passion of Pepper Dehner over the years. He has contributed several case series and reviews on various categories of these diseases for over 4 decades, with his earliest articles in the 1970s. He has written on all aspects of the disease including seminal articles on Langerhans cell histiocytosis (LCH) and their prognostic features, his experiences with regressing atypical histiocytosis, his encounters with malignant histiocytosis, and classic articles on juvenile xanthogranuloma. His contributions in the form of chapters in his 2 editions of the unique Pediatric Pathology textbook are no less important than his many articles. His experience with these lesions is highlighted in the 2 editions of the book, and the author and the audience is left wishing for more in a more current version. This article is more of a journey from descriptions and understanding of these various histiocytic syndromes to the current understanding and classifications with molecular inputs and recent advances. This article is dedicated to a master Clinician, Pathologist, and mentor whose contributions to the field of Pediatric Pathology makes him deserve beyond all doubt the title of "Father of Modern Pediatric Pathology."