Treatment of Advanced Systemic Mastocytosis with PKC412: The French Compassionate Use Programme Experience and Historical Comparison

Background

Advanced Systemic Mastocytosis (adSM) still have very poor prognosis. No standard of care is yet available. Midostaurin (PKC412) is a powerful TKI inhibit of VEGFR, FLT3 and most importantly the mutated CKITD816V and D816Y. Preliminarily results from an international phase II trial (Gotlib et al., Blood 2012) reported interesting results in this subgroup of patients. We report herein on the French experience of the compassionate use of PKC412 for the treatment of adSM and compare their outcome to matched adSM historical control patients (pts) who did not receive PKC412 (control group).

Methods

Over a period of 12 months (from August 2012, date of PKC412 Temporary Approval for Use in France), 22 pts received PKC412 and could be analysed. PKC412 100 mg twice daily was administered orally as continuous 28-day cycles until progression or unacceptable toxicity. Pts were evaluated according to the response criteria used in the recent phase 2 trial on midostaurin (Gotlib et al.). The overall survival (OS) of these 22 patients was compared to the OS of 42 age and WHO subcategories matched control adSM patients who were treated before PKC412 era.

Results

2 female and 20 male pts with a median age of 65 years [35-84] received midostaurin. Overall, 21 pts (95%) with adSM (5 ASM; 2 MCL; 1 MCS; 12 ASM-AHNMD; 1 SSM-AHNMD,1) and 1 pt progressive SSM. Median number of C-Findings was 3 (0-4). Hepato- and/or splenomegaly were present in 20 (91%) and 21 (95%) pts. Median tryptase level was 204 ng/l (85-2000). Median haemoglobin level, platelet and PMN counts were respectively 10.1g/dl (6.8-13.9), 117G/L (22-289) and 2.8G/L (0.3-17). Twenty (91%) pts had cKIT D816V mutation, 2 pts had cKITWT. ASXL1 and TET2 were mutated in 3/7 and 2/7 tested, respectively. Steroids, 2-chlorodeoxyadenosine and Interferon were administered in 9, 4 and 2 pts prior to midostaurin.

After a median exposure time of 6.9 [1.6-27.5] months, the overall response rate (ORR) was 77.2% including, major responses (n=13; 59%) (incomplete major in 8 pts, pure clinical in 5); partial response (n=5, 23%) (good partial in 3, minor partial in 2). Three patients were rapidly progressive (<2 months) and considered refractory to PKC412 (1 MCL, 1 MCS, 1 ASM-AHNMD). Death occurred in 4 pts (refractoriness 2 pts, AHNMD progression 2 pts). After a median follow-up of 7.4 months from PKC412 start, median OS was 24.4 months [12.6-34.2]. Patients with ASM seemed to better benefit from PKC412, however, no significant difference was found between the ASM and SM-AHNMD, probably due to the low patient’s number.

The control group consisted in 42 pts with a median age of 65.5 years [23-84]. There were 17 ASM-AHNMD, 21 ISM-AHNMD, 2 SSM-AHNMD, 1 CM-AHNMD and 1 MCL patients. Median tryptase level was 107ng/l [19-501]. Median haemoglobin level, platelet and PMN counts were respectively 12.1g/dl [8-15], 200G/L [10-1036] and 4.6G/L [0.5-24.3]. Thirty-three (79%) pts had cKIT D816V mutation, 7 pts were cKITWT. ASXL1 and TET2 were mutated in 6/29 (21%) and 7/29 (24%) of pts tested, respectively. Steroids, 2-CdA, interferon, imatinib, thalidomide have been used in 19, 21, 6, 4, and 6 pts respectively.

Survival distributions were estimated using the adjusted Kaplan-Meier method from the date of diagnosis to the last follow-up for the PKC412 treated and the control groups. Median survival time for PKC412 treated patients was significantly longer than control patients (p=0.04).

Conclusion

PKC412 is active in advanced SM. Despite the absence of complete remission, PKC412 gives survival advantage for patients with adSM over pts who did not receive the drug.