Systemic mastocytosis associated with acute myeloid leukaemia: report of two cases and detection of the c-kit mutation Asp-816 to Val

A subset of patients with systemic mastocytosis (SM) develop acute myeloid leukaemia (AML). However, little is known about the biology of such leukaem ias and their relationship to the mast cell (MC) lineage. We report on two female patients who suffered from SR;I and AML. According to FAB criteria, the leukaemias were classified as AML-M4 (patient 1) and AML-M0 (patient 2) . The coexistence of the two distinct neoplasms (AML and SMI was demonstrab le by immunostaining of serial hone marrow (BM) sections with monoclonal an tibodies (mAb). In particular, the MC infiltrates were found to react with mAb against MC-tryptase and MC growth factor receptor c-kit (CD117), but no t with mAb to CD15 or CD34. In contrast, the AML blasts were immunoreactive for C15 (patient 1) or CD34 (patient 2), but did not express tryptase, The c-kit point mutation Asp-Val at codon 816, considered to play a role in th e transformation of MC progenitors, was detected in patient 1 in a BM cell fraction containing 4% MC. However, no c-kit mutation was found in pure AML blasts (<1% MC). These findings argue against an evolution of the AML clon e from neoplastic MC or MC-committed progenitors.