title: Pseudoepitheliomatous hyperplasia mimicking invasive squamous cell carcinoma in extranodal natural killer/T-cell lymphoma: a report of 34 cases.
abstract: OBJECTIVE
  Pseudoepitheliomatous hyperplasia (PEH) is defined as a pattern of epidermal reaction. However, it has not yet been extensively documented in extranodal natural killer/T-cell lymphoma (ENKTL). The aim of our study was to analyse a series of ENKTLs concomitant with PEH mimicking squamous cell carcinoma (SCC).
  
  
  RESULTS
  We analysed 34 cases of ENKTL with PEH. In our study, the incidence of PEH was 3.8% in ENKTLs diagnosed over a 13-year period. All 34 cases presented with PEH, appearing as tongue-like projections of squamous epithelium into the underlying submucosa/dermis with variable depths and jagged borders. The keratinocytes sometimes showed a minor degree of cytological atypia, mostly in the stratum basale, and keratinocyte necrosis was absent. Atypical mitoses and a high nuclear/cytoplasmic ratio were absent. The submucosa and the squamous cell cords were also permeated by atypical lymphocytes.
  
  
  CONCLUSIONS
  ENKTL can be associated with PEH, and the atypical lymphoid cell population can be highly subtle, and therefore may be easily mistaken for SCC, leading to inappropriate therapy. A correct diagnosis requires awareness and recognition of this pitfall by recognizing the associated conditions listed above, which distinguish PEH from SCC.
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Yi-Hong
authors.initials: YH
authors.lastname: Ling
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Chong-Mei
authors.initials: CM
authors.lastname: Zhu
authors.affiliation: Department of Anaesthesiology, the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors.forename: Shi-Hong
authors.initials: SH
authors.lastname: Wen
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Rong-Zhen
authors.initials: RZ
authors.lastname: Luo
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Hui-Lan
authors.initials: HL
authors.lastname: Rao
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Su-Xia
authors.initials: SX
authors.lastname: Lin
authors.affiliation: Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.|Department of Pathology, Sun Yat-sen University Cancer Centre, Guangzhou, China.
authors.forename: Mu-Yan
authors.initials: MY
authors.lastname: Cai
mesh_terms: D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006965:Hyperplasia / Q000473:pathology; D054391:Lymphoma, Extranodal NK-T-Cell / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012867:Skin / Q000473:pathology; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000473:pathology; D055815:Young Adult
keywords: extranodal natural killer/T-cell lymphoma; histopathology; pseudoepitheliomatous hyperplasia