Evaluation of MRD Status by Flow Cytometry and PCR in Multiple Myeloma Elderly Patients Receiving Autologous Stem Cell Transplantation After Bortezomib-Supplemented Mobilization and Conditioning
Authors: Attolico Immacolata , Nuccorini Roberta , Fragasso Alberto , Pavone Vincenzo , Musto Pellegrino , Capalbo Silvana , Palumbo Gaetano , Specchia Giorgina , Carniti Cristiana , Corradini Paolo , Pascale Sara , Coluzzi Sabrina , Pizzuti Michele , Amendola Angela , Cimminiello Michele , Matturro Angela , Vertone Domenico , Filardi Nunzio , Olivieri Attilio 
Published: October 2019

Abstract
Abstract 4523
Autologous Stem Cell Transplantation (ASCT) is still an option for eligible patients with Multiple Myeloma (MM). High-dose melphalan (HDM: 200mg/m∧2) is the recommended conditioning before ASCT, but synergistic effects of Bortezomib (BOR) and HDM have been reported in vitro and in vivo.

PATIENTS AND METHODS:
We evaluated in 56 MM fit elderly patients (median age 65 yrs), the feasibility and efficacy (also in terms of evaluation of minimal residual disease: MRD) of a strategy, combining BOR, Cyclophosfamide (CY) and dexamethasone (DEX) as induction and mobilizing therapy (CY-BOR), for ASCT, with conditioning including BOR-HD-MEL. The patients achieving at least PR after 4 CY-BOR courses, were mobilized with BOR and DEX standard schedule with CY 3g/m∧2 (day 8). The pts collecting at least 2.5×10∧6CD34+/kg underwent ASCT with HD-MEL (day-1) and BOR (1.0mg/m∧2 on -6,-3,+1,+4), followed by thalidomide consolidation until Relapse/Progression. The MRD has been prospectively evaluated both by using 4 colour flow cytometry (FC), and by using patient-specific probes, by ASO-PCR. The percentage of plasma cells (PCs) has been evaluated both in in PBSC harvested and in bone marrow, with CD38, CD45, CD56, CD138, CD19, CD27, CD28, CD117, kappa and lambda, along different steps of therapy.

RESULTS:
Of 44 pts evaluable for response before ASCT, 32 (73%) achieved 3PR and 30 (68%) were mobilized: 29 (66%) collected3 2.5×106CD34+/kg and 25 underwent ASCT. Median time for PMN engraftment was 11 days (range 10–13) and 14 (range12–20) for PLT>=20.000/mcl. We observed grade 3 neuropathy in 3 patients and pneumonia during induction in 2 patients. At day +180 from ASCT 23 are evaluable for response and 21 for MRD: 3 pts have progressive disease (PD), 2 pts have a PR, 4 pts have a VGPR, 10 pts a nCR and 4 pts a CR. Four colour FC, in order to detect clonal plasmacells (cPCs) along several steps of treatment, showed that 3 pts (14%) achieved MRD negativity: 1/21 pts achieved MRD negativity at day +180 (cPC <0.01%), being positive after induction and at day +90 after ASCT; two patients were MRD negative after induction (one developed positivity at day + 180 and relapsed at day +365 from ASCT; the other one became positive at day +90 after ASCT and, is in CR at 10 months from ASCT). In 5 patients we evaluated MRD by PCR with patient-specific probes. One patient achieved clearance of MRD after induction and still maintains negative of PCR at 27 months from ASCT: this patient had positivity of MRD by flow cytometry after induction and at 90 months from ASCT, then became negative and is in CR. One became PCR negative after ASCT: flow cytometry was negative too and the patient is in CR at 10 months from ASCT; the remaining three patients are PCR positive: two of them experienced progression of disease.

CONCLUSIONS:
ASCT with HDM and BOR is feasible in older patients, with very high RRs and without major toxicities. We need a longer follow up and a larger number of pts to assess if these results will translate in a benefit in terms of outcome.

Disclosures:
Fragasso: Mundipharma: Honoraria.