Extramedullary Relapse of Multiple Myeloma - Plasma Cells Characteristics.

Multiple myeloma (MM) is the second most common hematological malignancy in the world. The introduction of new drugs (thalidomide, bortezomib, revlimid) has dramatically improved survival of MM patients, but MM still remains an incurable disease. Unfortunately, an increase in the incidence of extramedullary relapse of MM (EM), an aggressive mostly resistant entity with abysmal prognosis for patients has been reported. EM can affect any area of tissue - soft tissue involvement can be with or without relationship to bone. A recent study of 936 MM patients by Usmani et al (2012) reported presence of EM in the skin and soft tissues at the time of diagnosis while liver involvement was common at relapse or progression.

The objective of this study was to evaluate cytogenetic and flowcytometric data of available set of EM patients, and also to compare characteristics of plasma cells isolated from bone marrow and the extramedullary tumor.

In total, we evaluated 29 EM patients. Patients' characteristics were as follows: males/females 18/11, median age was 61.2 years, ISS stage I/II/III 1/5/23, IgG/IgA/ LC only 20/6/3. I-FISH analysis was performed on bone marrow (BM) samples obtained at the time of diagnosis of EM. Flowcytometric analysis was performed on plasma cells (PC) isolated from BM as well as the EM tumor.

Using flowcytometry, PC were identified as CD138+CD38+ leukocytes and surface expression of CD20, CD27, CD28, CD33, CD40, CD54, CD117, CD19 and CD56 were analysed on PC in whole BM and the tumor. We found statistically significant decrease of CD27 (60.0 vs. 9.1% positivity in BM vs. tumor, resp.; p<0.02) and CD19 (35.0 vs. 8.3%; p=0.001). Other markers were non-significantly decreased: CD33 (27.3 vs. 12.5%), CD40 (84.6 vs. 75.0%), CD54 (84.6 vs. 50.0%), CD117 (26.7 vs. 16.7%), CD56 (70.0 vs. 58.3%) while expression of CD28 was increased (13.3 vs. 33.3%) on tumor PC compared to BM PC.

In the BM PC, we found del(13)(q14) in 67% (18/27), del(17)(p13) in 22% (6/27), IGH rearrangement in 58% (11/19), t(4;14) in 33% (6/18), 1q21 gain in 58% (15/26), hyperdiploidy in 43% (10/23) of EM patients. The total number of aberrations per patient was: 0–1 aberration in 31%, 2–3 aberrations in 62%, 4 aberrations in 7% of MM patients BM.

For 4 patients, we were able to analyze both BM and the EM tumor. We found that in 2/4 patients, there was no agreement in chromosomal abnormalities found in the BM and EM tumor. The differences were in del(13)(q14) and IGH rearrangement. del(13)(q14) was present in all 100% (4/4) samples of BM but only 75% (3/4) of EM tumors. del(17)(p13) was present in 25% (1/4) of patients in the BM as well as EM. IGH rearrangement was present in 75% (3/4) of BM but only 25% (1/4) of EM. 1q21 gain was present in 50% (1/2) of patients in the BM and EM and hyperdiploidy was not present in the BM or EM tumor (0/2).

Chromosomal abnormalities connected to worse prognosis are more common in EM patients. PC phenotype seems to be different in cells obtained from BM and EM tumor. PC from EM tumor had significantly lower expression of CD27 and CD19. CD27 is a tumor necrosis factor receptor and plays a key role in regulating B-cell activation and immunoglobulin synthesis. Its low expression could be one of the main reasons for resistance in MM while loss of CD19 can create a proliferative advantage for the malignant plasma cell clone. Other interesting markers are CD54 and CD56 which were non-significantly decreased. CD54 also known as ICAM-1 plays a key role in stabilizing cell-cell interactions and migration, and CD56 (NCAM) is important for adhesion of PC to the bone marrow microenvironment. CD54 and CD56 lower expression may be the reason for EM development in MM but their role needs to be further elucidated.

This study was supported by grants NT12130, MSM0021622434, NS10207, NT11154.

No relevant conflicts of interest to declare.