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Leucocyte common antigen (CD45) and CD5 positivity in an “undifferentiated” carcinoma: a potential diagnostic pitfall
  1. Nyethane Ngo1,
  2. Kaushik Patel2,
  3. Peter G Isaacson3,
  4. Kikkeri N Naresh4
  1. 1Department of Histopathology, Hammersmith Hospital, Imperial College, London, UK
  2. 2Department of Histopathology, Kingston Hospital, London, UK
  3. 3Department of Histopathology, University College, London, UK
  4. 4Department of Histopathology, Hammersmith Hospital, Imperial College, London, UK
  1. Correspondence to:
 Professor K N Naresh
 Department of Histopathology, Hammersmith Hospital, Du Cane Road, London W12 0HS, UK; k.naresh{at}imperial.ac.uk

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CD45 is a transmembrane protein tyrosine phosphatase located on most haematopoietic cells. It has several isoforms, and haematopoietic cells express one or more of the isoforms—CD45RO, CD45RA and CD45RB.1,2 CD45 immunoreactivity is recognised to be highly specific for non–Hodgkin’s lymphomas.3,4 CD45-expressing non-haemopoietic tumours are very rare. This was first noted by McDonnell et al5 in 1987, who reported a primitive sarcoma expressing CD45. Subsequently, Nandedkar et al6 reported three cases of undifferentiated large-cell, possibly neuroendocrine, carcinomas expressing CD45. Two of them were lymph node metastasis and one was a pulmonary tumour. All the three cases expressed both CD45 and cytokeratin. Two of the cases behaved in an aggressive manner.6

In contrast to CD45, CD5 is expressed in thymic carcinoma and malignant mesothelioma.7,8 To the best of our knowledge, this is the first reported case of a carcinoma expressing both CD45 and CD5.

Case report

We report a patient in their 60s who presented initially with weight loss over 1 month and bilateral leg weakness with deterioration in mobility of 2 weeks’ duration. On examination, the patient was found to have bilateral cervical lymphadenopathy. Furthermore, the patient was an ex-smoker, and had been treated for chest infection 1 month earlier, but was …

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