title: Diagnosis and follow-up of keratoacanthoma-like lesions: clinical-histologic study of 43 cases.
abstract: BACKGROUND
  Keratoacanthoma (KA) is easily confused with squamous cell carcinoma (SCC) on a clinical or a histopathologic basis. However, KA undergoes spontaneous regression, whereas SCC does not.
  
  
  OBJECTIVE
  Our objective was to study the histopathologic features associated with clinical regression in KA-like lesions to support the therapeutic option.
  
  
  METHODS
  Forty-three biopsies of KA-like lesions were taken at patient admission. One month later, surgical excision was performed in 18 growing lesions. Regressing lesions were left untreated. Classic histopathologic features and diagnosis were blindly recorded in both biopsies and surgical specimens.
  
  
  RESULTS
  On a clinical and a histologic basis, 32 lesions were assessed as KA and 11 as SCC. Features that indicated malignancy were observed in both groups, but the probability of SCC was 31 times higher in tumors with five or more of such features. Several of the histologically atypical lesions were found to regress.
  
  
  CONCLUSIONS
  SCCs and KAs have more pathologic similarities than differences, especially in the proliferative phase. The combination of the most useful features did not allow the nosologic diagnosis in difficult cases but helped. Differential diagnosis was easier to determine after the 1-month follow up. Complete surgical excision should be indicated in nonregressing and growing lesions.
authors.affiliation: Dermatology Division, Department of Internal Medicine, School of Medical Sciences, UNICAMP, São Paulo, Brazil. renatafmagalhaes@uol.com.br
authors.forename: Renata Ferreira
authors.initials: RF
authors.lastname: Magalhães
authors.forename: Gabriela Torres
authors.initials: GT
authors.lastname: Cruvinel
authors.forename: Geórgia Fontes
authors.initials: GF
authors.lastname: Cintra
authors.forename: Maria Letícia
authors.initials: ML
authors.lastname: Cintra
authors.forename: Ana Paula Palu Baltieri
authors.initials: AP
authors.lastname: Ismael
authors.forename: Aparecida Machado
authors.initials: AM
authors.lastname: de Moraes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis; D016009:Chi-Square Distribution; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007636:Keratoacanthoma / Q000175:diagnosis* / Q000473:pathology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012871:Skin Diseases / Q000175:diagnosis* / Q000473:pathology; D012878:Skin Neoplasms / Q000175:diagnosis; D018709:Statistics, Nonparametric