Imatinib Mesylate (Page 10 of 11)

14.6 Aggressive Systemic Mastocytosis

One open-label, multicenter, Phase 2 study was conducted testing imatinib mesylate in diverse populations of patients with life-threatening diseases associated with Abl, Kit or PDGFR protein tyrosine kinases. This study included 5 patients with ASM treated with 100 mg to 400 mg of imatinib mesylate daily. These 5 patients ranged from 49 to 74 years of age. In addition to these 5 patients, 10 published case reports and case series describe the use of imatinib mesylate in 23 additional patients with ASM aged 26 to 85 years who also received 100 mg to 400 mg of imatinib mesylate daily.

Cytogenetic abnormalities were evaluated in 20 of the 28 ASM patients treated with imatinib mesylate from the published reports and in the Phase 2 study. Seven of these 20 patients had the FIP1L1-PDGFRα fusion kinase (or CHIC2 deletion). Patients with this cytogenetic abnormality were predominantly males and had eosinophilia associated with their systemic mast cell disease. Two patients had a Kit mutation in the juxtamembrane region (one Phe522Cys and one K509I) and four patients had a D816V c-Kit mutation (not considered sensitive to imatinib mesylate), one with concomitant CML.

Of the 28 patients treated for ASM, 8 (29%) achieved a complete hematologic response and 9 (32%) a partial hematologic response (PHR)(61% overall response rate). Median duration of imatinib mesylate therapy for the 5 ASM patients in the Phase 2 study was 13 months (range 1.4 to 22.3 months) and between 1 month and more than 30 months in the responding patients described in the published medical literature. A summary of the response rates to imatinib mesylate in ASM is provided in Table 23. Response durations of literature patients ranged from 1+ to 30+ months.

Table 23: Response in ASM
*
Patient had concomitant chronic myeloid leukemia CML and aggressive systemic mastocytosis (ASM).

Cytogenetic Abnormality

Number of Patients N

Complete Hematologic Response N (%)

Partial Hematologic Response N (%)

FIP1L1-PDGFRα Fusion Kinase (or CHIC2 Deletion)

7

7(100)

0

Juxtamembrane Mutation

2

0

2 (100)

Unknown or No Cytogenetic Abnormality Detected

15

0

7 (44)

D816V Mutation

4

1 * (25)

0

Total

28

8 (29)

9 (32)

Abbreviations: ASM, aggressive systemic mastocytosis; PDGFR, platelet-derived growth factor receptor

Imatinib mesylate has not been shown to be effective in patients with less aggressive forms of systemic mastocytosis (SM). Imatinib mesylate is therefore not recommended for use in patients with cutaneous mastocytosis, indolent systemic mastocytosis (smoldering SM or isolated bone marrow mastocytosis), SM with an associated clonal hematological non-mast cell lineage disease, mast cell leukemia, mast cell sarcoma or extracutaneous mastocytoma. Patients that harbor the D816V mutation of c-Kit are not sensitive to imatinib mesylate and should not receive imatinib mesylate.

14.7 Hypereosinophilic Syndrome/Chronic Eosinophilic Leukemia

One open-label, multicenter, Phase 2 study was conducted testing imatinib mesylate in diverse populations of patients with life-threatening diseases associated with Abl, Kit or PDGFR protein tyrosine kinases. This study included 14 patients with Hypereosinophilic Syndrome/Chronic Eosinophilic Leukemia (HES/CEL). HES patients were treated with 100 mg to 1,000 mg of imatinib mesylate daily. The ages of these patients ranged from 16 to 64 years. A further 162 patients with HES/CEL aged 11 to 78 years were reported in 35 published case reports and case series. These patients received imatinib mesylate at doses of 75 mg to 800 mg daily. Hematologic response rates are summarized in Table 24. Response durations for literature patients ranged from 6+ weeks to 44 months.

Table 24: Response in HES/CEL

Cytogenetic Abnormality

Number of Patients

Complete Hematological Response N (%)

Partial Hematological Response N (%)

Positive FIP1L1-PDGFRα Fusion Kinase

61

61 (100)

0

Negative FIP1L1-PDGFRα Fusion Kinase

56

12 (21)

9 (16)

Unknown Cytogenetic Abnormality

59

34 (58)

7 (12)

Total

176

107 (61)

23 (13)

Abbreviations: CEL, chronic eosinophilic leukemia; HES, hypereosinophilic syndrome; PDGFR, platelet-derived growth factor receptor.

14.8 Dermatofibrosarcoma Protuberans

Dermatofibrosarcoma Protuberans (DFSP) is a cutaneous soft tissue sarcoma. It is characterized by a translocation of chromosomes 17 and 22 that results in the fusion of the collagen type 1 alpha 1 gene and the PDGF B gene.

An open-label, multicenter, Phase 2 study was conducted testing imatinib mesylate in a diverse population of patients with life-threatening diseases associated with Abl, Kit or PDGFR protein tyrosine kinases. This study included 12 patients with DFSP who were treated with imatinib mesylate 800 mg daily (age range 23 to 75 years). DFSP was metastatic, locally recurrent following initial surgical resection and not considered amenable to further surgery at the time of study entry. A further 6 DFSP patients treated with imatinib mesylate are reported in 5 published case reports, their ages ranging from 18 months to 49 years. The total population treated for DFSP therefore comprises 18 patients, 8 of them with metastatic disease. The adult patients reported in the published literature were treated with either 400 mg (4 cases) or 800 mg (1 case) imatinib mesylate daily. A single pediatric patient received 400 mg/m 2 /daily, subsequently increased to 520 mg/m 2 /daily. Ten patients had the PDGF B gene rearrangement, 5 had no available cytogenetics and 3 had complex cytogenetic abnormalities. Responses to treatment are described in Table 25.

Table 25: Response in DFSP
*
5 patients made disease free by surgery

Number of Patients (n=18)

%

Complete Response

7

39

Partial Response *

8

44

Total Responders

15

83

Twelve of these 18 patients either achieved a complete response (7 patients) or were made disease free by surgery after a partial response (5 patients, including one child) for a total complete response rate of 67%. A further 3 patients achieved a partial response, for an overall response rate of 83%. Of the 8 patients with metastatic disease, five responded (62%), three of them completely (37%). For the 10 study patients with the PDGF B gene rearrangement, there were 4 complete and 6 partial responses. The median duration of response in the Phase 2 study was 6.2 months, with a maximum duration of 24.3 months, while in the published literature it ranged between 4 weeks and more than 20 months.

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