Genetic lesions in MYC and STAT3 drive oncogenic transcription factor overexpression in plasmablastic lymphoma

The mutational profile of plasmablastic lymphoma has not been described. We performed a targeted, exonic next-generation sequencing analysis of 30 plasmablastic lymphoma cases with a Bcell lymphoma-dedicated panel and fluorescence in situ hybridization for the detection of MYC rearrangements. Complete phenotyping of the neoplastic and microenvironmental cell populations was also performed. We identified an enrichment in recurrent genetic events in MYC (69% with MYC translocation or amplification and three cases with missense point mutations), PRDM1/Blimp1 and STAT3 mutations. These gene mutations were more frequent in Epstein-Barr virus (EBV)-positive disease. Other genetic events included mutations in BRAF, EP300, BCR (CD79A and CD79B), NOTCH pathway (NOTCH2, NOTCH1 and SGK1) and MYD88pL265P. Immunohistochemical analysis showed consistent MYC expression, which was higher in cases with MYC rearrangements, together with phospho-STAT3 (Tyr705) overexpression in cases with STAT3 SH2 domain mutations. Microenvironmental cell populations were heterogeneous and unrelated to EBV, with enrichment of tumor-associated macrophages (TAM) and PD1-positive T cells. PD-L1 was expressed in all cases in the TAM population but only in the neoplastic cells in five cases (4 of 14 EBV-positive cases). HLA expression was absent in the majority of cases of plasmablastic lymphoma. In summary, the mutational profile of plasmablastic lymphoma is heterogeneous and related to EBV infection. Genetic events in MYC, STAT3 and PRDM1/Blimp1 are more frequent in EBV-positive disease. An enrichment in TAM and PD1 reactive T lymphocytes is found in the microenvironment of plasmablastic lymphoma and a fraction of the neoplastic cells express PD-L1.

Diagnostic value of bone marrow core biopsy patterns in lymphoplasmacytic lymphoma/Waldenström macroglobulinaemia and description of its mutational profiles by targeted NGS

AIMS

The aim of this study was to describe the characteristics of the bone marrow infiltration found in a series of clinically defined lymphoplasmacytic lymphoma (LPL)/Waldenström macroglobulinaemia (WM) and IgM-monoclonal gammopathy of undetermined significance (MGUS) and to perform a targeted next-generation sequencing (NGS) for the identification of additional somatic mutations to MYD88p.L265P in LPL/WM.

METHODS

We have reviewed a series of 35 bone marrow biopsies from 28 patients with a clinical diagnosis of LPL/WM (24 cases) or MGUS (4 cases). Bone marrow infiltration characteristics by morphology, immunohistochemistry, flow cytometry (FCM), allele-specific real-time PCR for the detection of MYD88p.L265P mutation, targeted exonic amplicon-based NGS of 35 lymphoma-related genes and direct sequencing were analysed.

RESULTS

Our findings show that bone marrow trephine biopsy evaluation is superior to FCM in the identification of significant lymphoid infiltrates. A combined paratrabecular and interstitial infiltration pattern is the most common feature in LPL/WM while a patchy interstitial pattern characterises IgM-MGUS cases. MYD88p.L265P mutation was found by allele-specific-PCR in 92% of the LPL cases (22 out of 24) and 25% of IgM-MGUS cases (1 out of 4 cases). In addition to MYD88p.L265P somatic mutations in CXCR4, KMT2D, PRDM1/Blimp1, MYC and ID3 were found by NGS and direct sequencing in 4 cases.

CONCLUSIONS

In conclusion, bone marrow core biopsy evaluation is critical in the identification of unequivocal bone marrow infiltration by LPL/WM. In addition to MYD88p.L265P, somatic mutations in CXCR4, KMT2D, PRDM1/Blimp1, MYC and ID3 can appear in a fraction of LPL/WM.