Peritumoral fibrosis in basal cell and squamous cell carcinoma mimicking perineural invasion: potential pitfall in Mohs micrographic surgery.
BACKGROUND
Perineural invasion (PI) in cutaneous basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) is linked to an aggressive course. We describe a histologic mimic for PI that we termed peritumoral fibrosis (PF).


OBJECTIVE
To describe the morphologic changes associated with PF and to determine the incidence of PF and PI in Mohs frozen sections of BCC and SCC.


METHODS
All cases of BCC and SCC that were treated by Mohs micrographic surgery (MMS) at the Skin and Cancer Center, University of Florida College of Medicine, Gainesville, Florida, and the Center for Dermatology and Skin Surgery, Tampa, Florida, during the period from January 1, 2003, to August 1, 2004, were reviewed for the presence of PI and PF. The latter was defined as the presence of concentric layers of fibrous tissue that either surround and/or were surrounded by tumor formations mimicking perineural or intraneural invasion. Seven hundred six cases of BCC and 264 cases of SCC were surveyed. Eleven cases (10 BCC and 1 SCC) with equivocal areas were destained, and immunohistochemical staining with S-100 protein was performed, proving actual PI in all of these cases. Available original hematoxylin-eosin biopsy slides were correlated with the MMS frozen sections.


RESULTS
PF was noticed in 4.5% of SCCs and 5.8% of BCCs. The incidence of unequivocal PI was noted to be 2.6% in SCC and 2.1% in BCC.


CONCLUSIONS
We describe a specific pattern of fibrosis noted in BCC and SCC that we called PF. It shows concentric layers of fibrous tissue surrounding and/or surrounded by tumor formations and resembles carcinomatous perineural and/or intraneural invasion. Moreover, PF was found to be a sensitive marker for PI. Mohs micrographic surgeons should be aware of this phenomenon to avoid triggering unnecessary steps in managing these cases, such as irradiation.
Hassanein
Ashraf M
AM
Department of Pathology, University of Florida College of Medicine, Gainesville, 32610, USA. Hassan@pathology.ufl.edu
Proper
Steven A
SA
Depcik-Smith
Natalie D
ND
Flowers
Franklin P
FP
D002280:Basal Cell Carcinoma / Q000473:pathology*; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D003937:Diagnosis, Differential; D005355:Fibrosis / Q000473:pathology; D006801:Humans; D015580:Mohs Surgery; D009361:Neoplasm Invasiveness; D012878:Skin Neoplasms / Q000473:pathology*