Trastuzumab (Herceptin®) for Treatment of Refractory/Relapsed HER2 Positive Adult B-ALL: Results of a Phase II GRAALL Study

Abstract 1525

Trastuzumab (rhu-mAb-HER2, Herceptin®, F. Hoffmann-La Roche, Basel, Switzerland) is the humanized equivalent of the murine 4D5 monoclonal antibody targeted against the HER2 cell-surface receptor. In combination with chemotherapy, trastuzumab has significantly improved the outcome of women with HER2+ breast cancer. We have previously shown that HER2 surface antigen is up-regulated in around one third of adult B-ALL and is associated with chemoresistance in these patients (Chevallier et al, Haematologica, 2004). We report here for the first time the results of a Phase II study evaluating the safety and efficacy of trastuzumab in refractory/relapsed HER2 + adult B-ALL patients.

Prior to patient inclusion, HER2 positivity was assessed using multicolor flow cytometry with the phycoerythrin-conjugated HER2 Neu 24.7 antibody (BD) and a CD19+ CD45+low blast cell gating strategy. The mean fluorescence intensity (MFI) ratio was obtained by dividing the MFI of HER2 with that of its isotypic control. HER2 positivity threshold was defined by a ratio intensity (RI) >= 2. Also, HER2 oncogene amplification was assessed by FISH analysis using the HER2 DNA probe kit (Vysis, Downers Grove, IL, USA). Relapsed/refractory B-ALL patients aged >=18 years and with a HER2+ expression for at least 30% of the leukemic blast population in peripheral blood (PB) and/or bone marrow (BM) were included. Left ventricular ejection fraction has to be > 50%. All patients gave informed consent and the protocol was approved by the required regulatory authorities. The trial was registered at http://clinicaltrials.gov/ct no.NCT00724360. Trastuzumab was administered according to the approved schedule in breast cancer patients at 4 mg/kg intravenous loading dose followed by 2 mg/kg weekly. There was no corticosteroid premedication. Trastuzumab was provided by Roche.

Out of 50 patients screened for the HER2 expression, 15 patients (30%) (male n=8; female n=7), with a median age of 62 years (range: 24–80), have been included in the study between November 2006 and July 2011. This was considered as a very high-risk population: 2 patients had refractory disease after 2 induction courses, 2 patients were in first untreated relapse while 11 patients had a refractory first relapse or were beyond first relapse. Median percentage of HER2+ leukemic blast population was 94% (range: 0–100) in PB and 100% (range: 31–100) in BM. Surprisingly, no HER2 gene amplification was detected in samples assayed by FISH. Normal and complex karyotype were detected in 7 and 3 patients respectively. Three patients had a Phi+ B-ALL, and 1 patient a monosomy 7 (unknown karyotype n=1).

Currently, 3 patients are still receiving therapy. Considering the 12 other patients, the median number of trastuzumab infusions was 4 (1 month of treatment) (range: 2–20). No grade 3–4 toxicities were observed, with no cardiotoxic events. The overall response rate (CR or PR (decrease >=50% of blast population) or blast clearance in BM or PB) was 33%. No CR was observed. Two patients achieved partial response in BM (92% vs 12% after 9 infusions with loss of HER2 expression on blast population, total number of infusions (TNI) n=18); 25% vs 11% after 4 injections, TNI n=13) while blast clearance was observed in 2 other patients (96% vs 57% of blasts in BM after 8 infusions with loss of HER2 blast expression, TNI n=20; 20.5% vs 2% of blasts in PB after 3 infusions, TNI n=3).

In all, we conclude that trastuzumab in monotherapy can allow for some responses in this very high-risk refractory/relapsed HER2+ adult B-ALL population. Combination of trastuzumab with chemotherapy or other therapeutic monoclonal antibodies should be tested in the future. An updated follow-up of the study will be provided during the meeting.