Search

Mutational analysis of the c-kit gene in a patient with a previously undescribed variant of mast cell disease revealed a germline mutation, Phe522Cys, within the transmembrane portion of the Kit receptor protein. Transfection experiments revealed that the mutation caused ligand-independent autophosphorylation of Kit, which was inhibited by the tyrosine kinase inhibitor imatinib mesylate. The patient's bone marrow biopsy and aspirate displayed unique pathologic features with the presence of excessive numbers of mature-appearing mast cells and absence of aberrant mast cell surface expression of CD2, CD25, and CD35. Therapy with imatinib mesylate resulted in a dramatic improvement in mast cell burden and clinical symptoms. These results highlight the significance of the transmembrane region of Kit in activation of the molecule and its importance in mast cell development and suggest a role for screening for transmembrane c-kit mutations in patients with mastocytosis in association with the decision to use imatinib mesylate.

Mutations in the proto-oncogene c-kit cause constitutive kinase activity of its product, KIT protein, and are associated with human mastocytosis and gastrointestinal stromal tumors (GISTs). Although currently available tyrosine kinase inhibitors are effective in the treatment of GISTs, there has been limited success in the treatment of mastocytosis. 17-Allylamino-17-demethoxygeldanamycin (17-AAG), a benzoquinoid ansamycin antibiotic, which binds to heat shock protein 90 (hsp90) causes destabilization of various hsp90-dependent kinases important in oncogenesis. Treatment with 17-AAG of the mast cell line HMC-1.2, harboring the Asp816Val and Val560Gly KIT mutations, and the cell line HMC-1.1, harboring a single Val560Gly mutation, causes both the level and activity of KIT and downstream signaling molecules AKT and STAT3 to be down-regulated following drug exposure. These data were validated using Cos-7 cells transfected with wild-type and mutated KIT. 17-AAG promotes cell death of both HMC mast cell lines. In addition, neoplastic mast cells isolated from patients with mastocytosis, incubated with 17-AAG ex vivo, are selectively sensitive to the drug compared to the mononuclear fraction. These data provide compelling evidence that 17-AAG may be effective in the treatment of c-kit-related diseases including mastocytosis, GISTs, mast cell leukemia, subtypes of acute myelogenous leukemia, and testicular cancer.

Between May 1985 and July 1990, 45 patients (pts.) with primary (39) or recurrent (6) soft tissue sarcomas of the extremities (82%), torso (11%) and head and neck (7%) were treated with radiation therapy and conservative surgery. Seven pts. not amenable to conservative surgery underwent preoperative radiation therapy whereas 38 pts. underwent local excision and post-operative radiation therapy. Out of the 38 pts. managed by postoperative radiation, 24 (63%) showed negative surgical margins and 14 (37%) positive margins, their tumor being adjacent to vital structures. Preoperative radiation allowed conservative surgery in all 7 pts. with initially inoperable tumor; surgical margins were negative in 5 and positive in 2 pts. Twenty-six pts. (58%) had tumor greater than or equal to 5 cm (5-24) and 19 (42%) less than 5 cm (2.5-4.5) in diameter. High grade tumors (G2-G3) were reported in 41 pts. (90%). In pts. treated postoperatively the radiation dose was 64-66 Gy/32-33 fractions and the pts. treated preoperatively received a dose of 50 Gy/25 fractions. Median follow-up was 33 months and all pts. had a minimum follow-up of 12 months (12-72). Three pts. (6.5%) had local failure and 9 (20%) developed distant metastases with local tumor control. All distant metastases occurred in AJC stage IIIB, 9/18 (50%), with an increased frequency by tumor size. Overall local control and disease free survival rates at 5 years (product-limit method) were 93% and 73%, respectively. An evident decrease in disease-free survival rate (33%) was noted for stage IIIB pts.(ABSTRACT TRUNCATED AT 250 WORDS)