Critical ReviewKeratoacanthoma and Infundibulocystic Squamous Cell CarcinomaKossard, Steven MBBS, PhD, FACD*; Tan, Kong-Bing MBBS, MRCPath, FRCPA*†; Choy, Carolyn MBBS, FRCPA*Author Information From the *Skin and Cancer Foundation Australia, Sydney, Australia; and †Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, National University Hospital, Singapore. Dr. K-B. Tan was supported by a China Medical Board Fellowship. All figures are available in color online at http://www.amjdermatopathology.com. Correspondence: Steven Kossard, MBBS, PhD, FACD, Skin & Cancer Foundation Australia, 277 Bourke St., Darlinghurst. NSW 2010, Australia (e-mail: [email protected]). The American Journal of Dermatopathology: April 2008 - Volume 30 - Issue 2 - p 127-134 doi: 10.1097/DAD.0b013e318161310c Buy Metrics Abstract One of the major controversies in dermatopathology is the relationship of keratoacanthoma to squamous cell carcinoma. Leaders in the field remain polarized in their views. Carcinomas with distinct follicular pattern of differentiation have been described in reference to the isthmus as trichilemmal carcinomas, to the follicular bulb as pilomatricomal carcinomas, and to the stem cell or rapidly amplifying cell compartment as basal cell carcinomas (trichoblastic carcinomas). We have employed the term infundibulocystic or infundibular squamous cell carcinoma to identify a subset of squamous cell carcinomas that demonstrate this pattern of differentiation. The recognition of infundibular squamous cell carcinoma is important in that well-differentiated examples are likely to have been diagnosed as keratoacanthoma, whereas moderately or poorly differentiated tumors would be more often reported as squamous cell carcinomas, leading to underrecognition of these infundibular variants of squamous cell carcinoma. The descriptive term infundibulocystic or infundibular squamous cell carcinoma may help to better define an alternative follicular-based pathway to squamous cell carcinoma distinct from the more common evolution from solar keratoses and also refine the classification of keratoacanthoma. © 2008 Lippincott Williams & Wilkins, Inc.