BRAF V600E Targetable Mutation in Relapsed/Refractory Multiple Myeloma (R/R MM) Patients: A High Incidence in R/R MM Detected Using Cell Sorting Screening

Background:

The oncogenic BRAF V600E mutation activates the MAPK signaling pathway resulting in cell growth and survival of tumor cells carrying the mutation. Targeting BRAF has shown its efficacy in metastatic melanomas. BRAF V600E mutation has been described in multiple myeloma (MM), with an incidence of 4-10% in previous reports. We report here the incidence of BRAF mutations in a series of MM patients treated at our center.

Methods:

From February 2012 to March 2016, 94 MM patients were tested for BRAF mutations. Eighty-one samples came from patients with relapsed/refractory MM (R/R MM) and 13 samples from newly diagnosed patients. Eighty-eight samples were collected from bone marrow aspirates, 3 from extramedullary plasmacytoma biopsies, 1 from pleural effusion, and 2 from peripheral blood. Targeted sequencing for BRAF mutations using Sanger direct sequencing or targeted next generation sequencing were performed on all samples after CD138 cell (after 2015). In addition, NGS was performed for 2 patients. From 2012 to 2015, we used material obtained from scraping bone marrow smears with > 20% plasma cells. Since 2015, we began using immunomagnetic cell-sorting based on the CD138 cell surface marker (Stem Cells®).

Results:

BRAF mutations were detected in 8 samples out of the 84 that could have been screened (9.5%). When considering only the relapsed/refractory population, the incidence of BRAF mutations was 10.8%. One sample had the inactivating D594N BRAF mutation and the other 7 had the V600E BRAF mutation. The 8 mutated patients had relapsed/refractory MM at the time of analysis. Of note, 5 out of the 8 mutated patients (62.5%) had an IgA MM. Seventy-six samples had no BRAF mutation detectable. Ten samples were not tested because of the small percentage of MM cells on the bone marrow smears. The failure rate was 16% with the scraping technique and 3.4% with the sorting cell technique. Five out of 7 patients harboring the V600E BRAF mutation were treated with a BRAF inhibitor in different clinical trials. One mutated patient could not be treated due to exclusion criteria related to an underlying condition (terminal renal failure requiring chronic hemodialysis) and one patient received allogeneic stem-cell transplantation at relapse. No BRAF mutation was detected in the 13 newly diagnosed patients.

Conclusion:

Our results show that BRAF screening is feasible in routine practice and can help orienting therapy in relapsed/refractory MM patients. The incidence of 9.5% that we found in our series compares favorably with previously published results, and we observed a slightly increased incidence of 10.8% in the R/R population. The cell sorting technique seems to be more effective than the scraping technique for MM sample DNA acquisition and BRAF mutation screening. Results of BRAF inhibitors therapy in MM are eagerly awaited.