Systemic mastocytosis is a rare disease (0.3 new cases in 105 of the general population). The systemic form of the disease without skin involvement is reported in about 50% of the cases. The term mastocytosis refers to a group of disorders characterized by abnormal accumulation of mast cells in one or more organs. The most commonly affected organs are skin, bone marrow and gastrointestinal system. We present two cases of systemic mastocytosis concerning two male patients aged 65 and 66 years old, one of whom presented without skin involvement. Diagnosis was established on the ground of histological, histochemical and immunohistochemical examination of bone marrow biopsies in both cases. We emphasize the importance of bone marrow biopsy for diagnosis and discuss the utility of histochemical stains, such as chloroacetate a-naphthol esterase and Giemsa, as well as of the immunostains CD117, CD2, and Stem Cell Factor, for the identification of the neoplastic mast cells. Several aspects of the disease, such as diagnostic criteria, molecular characteristics and prognosis, are also discussed.

Key words: Systemic mastocytosis, bone marrow biopsy, histochemistry, immunohistochemistry.

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