Indolent Clinical Behaviour of Primary Cutaneous Diffuse Large B‐cell Lymphoma, Leg Type, with Double MYC and BCL6 Gene Rearrangement

In 2010, an 83-year-old woman presented with a 5-cm nodule on her right knee, diagnosed as primary cutaneous-diffuse-large-B-cell lymphomas-leg type (PCDLBCL-LT) that suffered complete remission (CR) after treatment with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisolone (R-CHOP; six cycles). Eight years later three small nodules appeared at the same site (Figs 1A and 2A). Again, after surgery, chemotherapy (R-mini-CHOP×3) and local radiotherapy, CR was achieved without evidence of recurrence two years later. This clinical behaviour is surprising since the prognosis of most PCDLBCL-LT patients is usually poor, with multiple cutaneous/extracutaneous recurrences.1 Notwithstanding, spontaneous regression of some cases has been reported.2 Histologically, the 2010 cutaneous biopsy consisted of a dermis and subcutaneous tissue diffusely infiltrated by medium-sized round cells with scant cytoplasm, hyperchromatic nuclei and small nucleoli (Fig 1). Apoptotic cells and mitotic figures were found. In contrast, the 2018 lesion showed larger cells with abundant cytoplasm, round nuclei and rather prominent nucleoli (Fig 2). Epidermis was spared in both specimens. The immunophenotype of both samples was identical, showing neoplastic cells CD20, BCL6, CD10, BCL2 and MYC and were negative for CD30, Cyclin D1, SOX11, TdT, MUM1, p53 and EBV (EBER) (Figs 1 and 2). The proliferation activity (Ki-67) was high (almost 100%). Based on morphology and immunophenotype, the diagnosis of DLBCL of GC-phenotype (according to the Hans algorithm) was made in both instances. Given the double expression of MYC and BCL2, fluorescent in situ hybridization (FISH) studies for BCL6/BCL2 and MYC genes were performed. Translocations of both MYC/BCL6 genes were found. Interestingly, a biallelic and a monoallelic MYC gene rearrangement was detected in the first and second biopsy respectively (Figure S1). To the best of our knowledge, this finding has not been described so far in PCDLBCL-LT or systemic high-grade B-cell lymphomas with MYC/BCL2/BCL6 rearrangements (high grade B cell lymphoma [HGBCL]-DH/TH), although it has been reported for the DUSP22 gene in anaplastic large cell lymphomas.3 Next-generation sequencing (NGS) studies identified a BCL6–IGL rearrangement, with identical breakpoints on BCL6 and IGLJ1 in both samples. Rearrangements of BCL6 to IGL or to other non-IG partners probably have an influence on prognosis.4 Interestingly, a MYC–IGH translocation was identified in the 2010 sample but not at relapse. Moreover, a fusion (using a fusion MYC–IGH probe) was identified at first diagnosis, but not at relapse, confirming NGS results (Figure S2). It is well known that the majority of MYC rearrangements in HGBCL-DH/TH have non-IG partners.5 HGBCL-DH/TH are usually of GC phenotype6 while PCDLBCL-LT are typically of ABC phenotype. Of PCDLBCL-LT, 16% show CD10 expression, inversely correlated with the presence of MYC gene translocation.7 Over 90% of cases of PCDLBCL-LT express BCL2, and about two thirds of them are double expressors. Furthermore, MYC rearrangement has been reported in 32% of the cases,1 with only two cases described so far of double rearrangement.7 Both double expression of BCL2/MYC or MYC gene rearrangement in PCDLBCL-LT patients are related to poor outcome.7 The presence of a second hit involving the BCL6 gene did not seem to make any difference in cases with MYC gene rearrangements.7 Prognosis of HGBCL-DH/TH depends not only on the partner of MYC gene rearrangements but also on whether BCL2 or BCL6 gene is the second hit.8 Next-generation sequencing also showed the same rearrangements of IGH and IGK genes (IGHJ4–IGHD3-22, IGKJ2–IGKV1-39, intronRSS–Kde and IGLJ1–IGLV3-21) in both samples although they differed in their somatic mutation repertoire. Mutations of SMARCA4 and KMT2D genes were detected in the first biopsy but not in the second one, while FAT1 gene mutation appeared only in the recurrence. The remaining gene alterations (CD79B, TNFAIP3, HIST1H1E and PIM1) were present in both (Table SIII). The MYD88 p.L265P mutation, present in about 60% of PCDLBCL-LT cases, and related to poor prognosis,9 was not found here, neither by quantitative reverse transcription polymerase chain reaction (qPCR) nor NGS. Other genes previously reported in PCDLBCL-LT were present both in the first biopsy and at relapse (CD79B, HIST1H1E and PIM1).9 Mutations on the TNFAIP3 (A20) gene have not been previously reported in PCDLBCL-LT, even though deletions of this gene are frequent.9 Interestingly, in the first biopsy, mutation of genes related to germinal centre B-cell origin lymphomas, such as SMARCA4 or KMT2D (MLL2) was found. Significance of mutations in FAT1 is still not known in DLBCLs. Interestingly, biallelic CDKN2A gene deletions were identified in both samples. These data imply that the lymphoma diagnosed in 2018 was a bona fide recurrence of the one diagnosed in 2010, demonstrating that both tumours share a common clonal progenitor but were subjected to divergent evolution (Figure S3). Tumours such as PCDLBCL-LT are aggressive lymphomas characterized by a proliferation of immunoblastic-like large neoplastic B cells of ABC phenotype which characteristically show both MYD88 p.L265P mutations and CDKN2A gene deletions. Secondary skin involvement by a systemic HGBCL-DH/TH, Burkitt lymphoma, mantle cell lymphoma and systemic follicular lymphoma transforming into HGBCL-DH/TH could be ruled out both clinically and immunophenotypically. Nevertheless, primary cutaneous follicular lymphoma (PCFCL) with a diffuse pattern and predominance of large cells should be taken into consideration. These usually occur in the head and neck or the trunk. Histologically, a mixture of centrocytes and centroblasts with a large amount of small bystander T cells and scattered CD23- or CD21-positive residual follicular dendritic cells is seen. They are characteristically BCL2- and CD10-negative. BCL2-positive cases with CD10 expression and BCL2 gene translocation makes it advisable to rule out a systemic origin. Only mutations in the TNFRSF14 gene have been reported in PCFCL, usually in combination with 1p36 deletion.10 All these facts together allowed us to exclude the diagnosis of PCFCL with a diffuse pattern. In conclusion, we report a PCDLBCL-LT that showed peculiar immunophenotype, molecular background and a remarkably indolent clinical behaviour. These data suggest that the group of PCDLBCL-LT is more heterogeneous than previously thought. This work was supported by grants from the Instituto de Salud Carlos III (ISCIII) of the Spanish Ministry of Economy and Competence (MINECO, RTICC ISCIII and CIBERONC) (SAF2013-47416-R, RD06/0020/0107, RD012/0036/0060 and Plan Nacional I+D+I: PI17/2172, PI16/01294 and PIE15/0081), AECC and the Madrid Autonomous Community. Informed written consent has been obtained. Studies have been performed according to the Declaration of Helsinki. The procedures have been approved by a local ethics committee. Date 08-11-2018; Approval number: PICO75-18_FJD; CEIm-FJD. Dr. Piris is sponsored by TAKEDA. The other authors have no conflict to declare. Table SI. Panel of antibodies investigated in this study Table SII. List of probes of the custom B-cell lymphoma panel. Table SIII. Somatic mutations found in biopsies taken in 2010 and 2018 respectively. Name of the gene, alteration and allele frequency of the change are indicated. Data S1. Material and methods. 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