Clinical Implications of MYD88 and CXCR4 in Patients with Waldenström's Macroglobulinemia

Background

Waldenström's macroglobulinemia (WM) is a rare B-cell neoplasm defined as lymphoplasmacytic lymphoma with bone marrow infiltration and monoclonal IgM in the serum. More than 90% of WM patients carry a point mutation L265P in the MYD88 gene and concurrently, almost one third of MYD88^L265P-positive patients harbor frameshift (WHIM-FS) or non-sense (WHIM-NS) mutation in gene CXCR4. The mutations in CXCR4 result in premature stop codons and in shortening of CXCR4 protein product. Incomplete C-terminal domain of CXCR4 chemokine receptor is known to hyperactivate CXCR4-mediated signalization. The presence and type of mutation in genes MYD88 and CXCR4 appears to be significant in diagnostics and prognostic stratification of WM patients and it also influences the clinical manifestation of the disease.

Aims

To analyze mutational status of MYD88 and CXCR4 genes in patients with WM, to compare our results with laboratory parameters and to evaluate the prognostic stratification of the patients according to MYD88 and CXCR4 mutational status.

Methods

Analyzed DNA was isolated from mononuclear fraction of bone marrow or peripheral blood cells at the time of diagnosis. Mutational status of analyzed genes was determined using allele-specific PCR (in the case of MYD88) and using direct Sanger sequencing (in the case of CXCR4). All found mutations were confirmed by specific cleavage with restriction endonucleases at defined conditions.

Results

We analyzed 23 patients with WM. All patients were MYD88^L265P-positive (100 %), and 7 of them (30,4%) were also CXCR4 mutants (1 patient harbored WHIM-FS mutation and 6 harbored WHIM-NS mutation). CXCR4 mutations were associated with more aggressive disease: higher ISSWM score (low 0/intermediate 1/ high 6 risk), anemia (7/7), hyperviscosity syndrome (2/7) at time of diagnosis. CXCR4^WHIM-WT patients were often asymptomatic (5/16) with lower ISSWM score (low 5/intermediate 5/ high 6 risk) but with common adenopathy (11/16). CXCR4 mutations were also associated with worse treatment response (2 CXCR4^WHIM-MUT patients were refractory to initial therapy and needed 2^nd line treatment, 3 patients had only partial response to first-line therapy, one patient died after 2^nd cycle due to abdominal septic complication and only one patient reached VGPR). Progression-free survival in treated patients was 32 vs. 8 months in CXCR4 mutants.

Conclusion/summary

The mutational analysis of MYD88 and CXCR4 genes is essential for the diagnostics and prognostic stratification of patients with WM and it allows a deeper understanding of the molecular pathogenesis of the diseases. CXCR4 mutations were found in nearly one third of WM patients. In accordance with published data, we confirmed that CXCR4 mutations are associated with more aggressive disease presentation and thus affect treatment outcome. On the contrary CXCR4^WHIM-WT patients have more indolent course of the disease.

This work was supported by grant IGA-LF-2018-004 and MH CR - RVO (FNOL, 00098892).