Chimeric Antigen Receptor T Cell Therapy in the Relapsed or Refractory Multiple Myeloma with Extramedullary Disease--a Single Institution Observation in China

Background: Extramedullary disease (EMD) is characterized as the presence of myeloma cells invasion outside the bone marrow in a patient with multiple myeloma (MM), it may be found 6%~8% in de novo patients, and 10% to 30% in relapsed or refractory (R/R) MM patients across the overall disease course (Joan Blade et al. 2011, Matthew Weinstock et al. 2013 and 2015, Cyrille Touzeau et al. 2015). EMD was considered as high-risk group of myeloma and is associated with adverse prognosis and the management is particularly challenging. Here we discuss and improve the understanding of the clinical characters and prognoses of the R/R MM with EMD in the treatment of CAR T therapy, illustrate our experience in a single institution. Methods: LCAR-B38M is a Chimeric antigen receptor (CAR) T cell therapy with 4-1BB as the co-stimulator, a dual epitope-binding CAR T cell therapy directed against 2 distinct B cell maturation antigen (BCMA) epitopes. In total of 57 patients were treated in China from The Second Affiliated Hospital of Xi'an Jiaotong University (LEGEND-2, NCT03090659), 17 patients with R/R MM with EMD were included and received the CAR T treatment. The study was initiated on March 30, 2016, and the analysis reported here is from a data cutoff date of July 31, 2019, the detailed treatment schema was presented in the former paper (Zhao et al, 2018). Results: Overall, 17 (29.8%) of 57 treated patients with EMD were included in our CAR T treatment. The median age of R/R MM patients with EMD (EMD group) and without EMD (non-EMD group) were 55 (range, 27-72) and 53.3 (range, 42-73) years old respectively, and the median number of prior therapy lines were 3 (range, 1-6 and 1-9) in both groups. There were no statistical difference in the proportion of male and female patients, median time from initial diagnosis and ISS stage in EMD group and non-EMD group. The Eastern Cooperative Oncology Group (ECOG) scores of patients receiving CAR T treatment were 0-2 points, the proportion of ECOG 1-2 points in EMD group were higher than non-EMD group (P < 0.05, R=0.1474, 95% CI, 0.03 to 0.73). IgG and IgA subtype were the main types in the non-EMD patients while the light chain type was more frequently seen in EMD group (P = 0.014, OR=0.1886, 95% CI, 0.05 to 0.66). The overall response rates (ORR) in the EMD group and non-EMM group were 82.4% and 90% respectively (Fig 1 A), and there were no significant difference in the median time to the first response and the best response between the EMD group and non-EMD group(P > 0.05). At cutoff, the median follow-up was 25 months, the median progression-free survival (PFS) in EMD group and non-EMD group were 8.1 months and 25 months (P < 0.001, R=0.32, 95% CI, -0.19 to 0.84), and the median overall survival (OS) were 13.9 months and not reached (P = 0.0019, R=4.833, 95% CI, 1.91 to 12.22), survival curves were shown in Fig 1 B, C . Conclusions: LCAR-B38M is a highly effective therapy in R/R MM patients with EMD and without EMD, and both groups had similar response time and reached a high ORR rate. R/R MM patients with EMD demonstrated a poor prognosis and they may lost their best response in a relatively shorter time compared with the patients without EMD. With a median follow-up of 25 months, LCARB38M manifested a relatively durable therapeutic effect in this high-risk R/R MM patients with EMD. No relevant conflicts of interest to declare.