[A-leukemic caecal myeloid sarcoma: a difficult diagnosis].

Myeloid sarcoma is a malignant neoplasia composed of abnormal myeloid or monocytic cells, often localized in bones, but also rarely in extra-medullary sites such as lymph nodes, skin and soft tissue. We report a case of caecal myeloid sarcoma, diagnosed in a 60 year old woman who complained from abdominal pain and weight loss, in absence of any medullary disorder. Initially misdiagnosed as a B lymphoma because of a weak positivity for CD79a, the diagnosis of primitive caecal myeloid sarcoma was eventually established after further investigations showing a positivity for lysozyme and myeloperoxidase. This report of such a rare clinical and pathological presentation of a myeloid sarcoma underlines a difficult differential diagnosis for which adequate immunohistochemistry, including lysozyme and myeloperoxydase is mandatory.