Epidemiology
To date, 12 studies have analyzed PT-PEL, with a total of 13 cases. Patient characteristics, in addition to morphological, immunohistochemical and molecular features and clinical data, including treatment and outcome, are summarized in Table 1.
Table 1 Clinicopathological features of primary effusion lymphoma in post-transplant patients
Ref/ age, sex, ethnicity/
|
Serology/ possible source of HHV8 infection
|
Transplanted organ/
time from TP to PEL diagnosis
|
IS therapy/
HAART therapy
|
KS or other malignancies/
pre-TP or post-TP
|
Site of PEL/
BM involvement
|
Histology
|
IIC/EBER
|
Molecular data
|
Therapy
Survival from PEL diagnosis
|
Jones 1998
59/M Haitian
|
HIV-; no drug abuse; no sex with men
|
Heart/ 94 mos
|
AZA + CYA+ prednisone
|
KS (5 mos after TP)
|
Bilateral pleural effusions/
BM NA
|
Large plasmacytoid cells, moderate basophilic cytoplasm, prominent multiple nucleoli
|
CD30+ EMA+ CD38+ CD10- CD19- CD20- CD79a- CD3- CD5- CD45RO- CD11b- CD13- CD14- CD33- CD45- CK- EBVLMP1- EBER-
|
IGH+,
HHV8 DNA+
EBVDNA-
|
CYA reduction
Cycloph+ VCR+ prednisone (1cy).
Bleo.
CHOP (1cy).
Ifo+eto (2 cy).
Death 6 mos later.
|
Dotti 1999
56/M/unknown
|
HCV+ HIV -
HBV-
|
Heart/42 mos
|
AZA+ CYA+steroid
|
No
|
Peritoneal effusion
BM positive at molecular analysis
|
Medium, large-sized cells, abundant basophilic cytoplasm, convoluted nuclei, large and multiple nucleoli
|
CD45+ CD38+ CD138+ HLA-DR+ CD30+
CD34- CD13-CD33- CD3-CD2- CD5-CD7- CD10-CD20- CD19-CD56- k- l-
|
IGH+ HHV8 DNA integration
EBV genome integration
11q23 deletion No BCL6 c-MYC ALL-1 rearrangements. No Bcl2/IGH translocation.
|
CYA reduction, AZA stopping.
No CT (for poor performance status).
Death 1 mo later
|
Boulanger 2008
57/M/African
|
HIV-
HHV8+ (before TP)
|
Kidney/44 mos
|
TC+ MMF+ prednisone.
5 mos after TP: KS progression despite MMF stopping, TC and prednisone reduction+CT (dauno+ docetaxel+ bleo)
24mos after KS onset: TC stopping+ RAPA with partial KS remission. At PEL diagnosis RAPA blood level 12ng/ml
|
Disseminated KS (5 mos after TP)
|
Right pleural effusion
BM NA
|
PEL morphology
|
CD138+ CD38+ HHV8+ EBER- CD3- CD20-
|
IGH+ TCR-
HHV8 DNA+ (PCR)
Oligoclonal HHV8 episomes+
|
CHOP + bleo (4 cys)
Death 8 mos later
|
Boulanger 2008
63/M/African
|
HIV-
HHV8+ (before TP)
|
Kidney/54 mos
|
CYA+ MMF+ prednisone+ Anti CD25 moAb
3 mos after TP Meth (for rejection).
14 mos after TP CYA converted to RAPA (for renal graft impairment). At PEL diagnosis RAPA blood level 8.5 ng/ml
|
No
|
Cardiac tamponade
BM NA
|
PEL morphology
|
CD30+ CD138+ HHV8+ EBER- CD20- CD3-
|
IGH- TCR-
Oligoclonal HHV8 episomes+
|
Cidofir
Death 1 mo later
|
Melo 2008
67/M/unknown
|
NA
|
Kidney/132 mos
|
AZA+ CYA+ prednisone
|
No
|
Left pleural effusion
BM NA
|
Large hyperbasophilic cells with multiple nucleoli
|
CD45+ CD38+ CD138+
Negativity for B and T cells markers
|
HHV8+ EBV+ (PCR)
|
Cycloph+VCR+prednisone
CY and AZA stopped
RAPA
(blood level 7ng/ml)
|
Testa 2010
55/M/unknown
|
HIV- HBV- HCV- HAV-CMV-
HSV2-EBVDNA-
HBVDNA-
HCVRNA-
CMVDNA-
HSVDNA-
HHV8-
|
Liver/12 mos
|
TC+
MMF
|
No
|
Massive neoplastic infiltration of lungs, pleura, heart, IC muscles, around large vessels, Gerota fascia, omentum.
Sclerosing peritonitis of stomach, intestine, liver
BM NA
|
Large cells, prominent nucleoli, abundant basophilic cytoplasm
|
CD138+ EMA+ CD43+ vimentin+ HHV8+ kappa/lambda polyclonal ki67>90% CK- CD20- CD3- CD45- EBVLMP1- CD56- CD57- MPO- CD34- Melan-A- CD99- Desmin- CD68-TdT- CD30- calretinin-
|
HHV8DNA+
EBVDNA- HSVDNA- CMVDNA- HHV6-
|
Diuretics
Death 4 mos later
Autopsy performed
|
Rose 2012
42/M/Italian
|
HIV- HBV- HCV-
|
ASCT/276 mos
|
Myeloablative conditioning (Cicloph+TBI);
chronic GVHD treated with CYA prednisolone, PUVA, THA.
24 mos after TP: pericarditis; THA stopped
|
No
|
Marked peritoneal effusion,
small pleural effusion.
Constrictive pericarditis
BM NA
|
Atypical lymphoid cells
|
CD45+ CD138+ TdT- CD34- MPO- CD3- CD5- CD20- CD79a-
CD30- ALK1-
Ki67 100%
|
PCR: HHV8+
|
PericardiectomyDeath 2 weeks later
|
Shi 2012
60/M/Chinese
|
Serology pre-transplant: NA
Serology at PEL diagnosis: HIV- HHV8+
|
Kidney/120 mos
|
Long-term IS therapy (NS)
|
No
|
Bilateral pleural effusion, peritoneal effusion
BM negative
|
Large cells with large nuclei, prominent nucleoli, scanty cytoplasm
|
HHV8+ CD30+ CD45+ vimentin+ EMA+ CD3- CD15- CD20- CD43- CD79a-CD45RO- CK-ALK1- EBVLMP1-
|
IGH+
IGL+
|
CT (endoxan, farmorubicin, oncovin, prezolon). Death 4 mos later
|
Christenson 2015
72/M/unknown
|
HIV- EBV DNA- CMV-
No drug abuse; no sex with men; no link with HHV8 endemic areas
|
Liver/120 mos
|
TC (119 mos) changed to RAPA 1 mo prior PEL (due to altered renal function)
|
SCC of head and neck (surgery, CT, RT)
|
Pleural effusion
BM NA
|
Large plasmacytoid cells, large convoluted nuclei, prominent nucleoli
|
CD45+ CD30+ CD38+ MUM1+ HHV8+ EBER -
|
NA
|
Rapamycin maintained+
pleural drainage+
intrapleural cidofovir.
Due to cidofovir intolerance, bortezomib+
Doxo.
Death 7 mos later
|
Kalogeraki 2015
49/M/unknown
|
HIV-
|
Kidney/340 mos
|
Prolonged IS therapy
|
No
|
Peritoneal effusion
BM NA
|
Large cells with high N/C ratio, pleomorphic nuclei, prominent nucleoli, amphophilic cytoplasm
|
CD3+ CD138+ PAX5+ CD30+ CD45+/-
HHV8+ (in situ hybridization) EBER-
CK- EMA- CD2- CD5- CD19- CD20- CD43- CD79a- ALK1- TIA1-
EBVLMP1-
|
IGH+ TCR+
|
CHOP
Alive at 10 mos
|
Cain 2018
29/M/unknown
|
HIV+
HBV- HCV – CMV-
|
Kidney/24 mos
|
TC+
HAART
|
Nodal KS identified at autopsy
|
Pleural effusion lymph nodes spleen liver
heart kidney lung
BM NA
|
Intravascular large plasmacytoid and immunoblastic cells
|
CD45+ MUM1+
HHV8+ EBER+ CD20- CD79a- CD19 PAX5- CD2- CD3- CD5- CD7- CD4- CD8- ALK- MPO- CD138- kappa- lambda- IgM- IgD- CD34- CD117- CD30- EMA- CD10- Bcl6- TdT-
|
IGH and TCR NA for poor DNA quality
|
Death 2 weeks after admission
Autopsy performed
|
Kugasia 2018
63/M Haitian
|
Remote history of polysubstance abuse
Pre-transplant: HIV- EBV- HHV8-
Post-transplant:
HIV- EBV- HHV8+
|
Heart/5 mos
|
TC+ prednisone
|
Cutaneous KS
(pre-TP) treated with RT.
KS recurrence at PEL diagnosis
|
Left pleural effusion
BM positive
|
Large atypical cells with high N/C ratio, prominent nucleoli
|
CD45+ CD30+ HHV8+ CD138+ MUM1+ CD20- PAX5- CD4- CD8- CD56- ALK1- EBVLMP1- EMA- BCL2- BCL6- cyclin D1- CD10- calretinin -WT1- Ber-EP4-
|
NA
|
Cycloph, VCR, prednisone, brentuximab
TC changed to sirolimus.
(HHV8 undetectable)
Death 14 mos later for acute graft rejection
|
Zanelli 2019
42/M/Italian
|
HIV-
HHV8-
EBV-
|
Small bowel/7 mos
|
TC+
Anti-CD52 moAb
|
No
|
Multiple gastric and duodenal polyps
BM negative
|
Large cells with eccentric nuclei and prominent nucleoli
|
CD138+ CD38+ CD30+ HHV8+ EBER+
Ki67 70% EMA+ lambda+
CD20- CD79α- PAX5- CD3- CD5-
|
NA
|
Death 1 mo later
|
Legends: ASCT: allogenic stem cell transplant; Aza: azathioprine; bleo: bleomycin; BM: bone marrow; CHOP: cyclophosphamide, doxorubicin, prednisone, vincristine; Cy: cycle; CYA: cyclosporine; Cys: cycles; Cycloph: cyclophosphamide; CT: chemotherapy; Dauno: daunorubicin; Doxo: doxorubicin; EBV: Epstein Barr virus; Eto: etoposide; GVHD: graft versus host disease; Ifo: ifofosfamide; IGH: immunoglobulin heavy chain; IGL: immunoglobulin light chain; IS: immunosuppressive; KS: Kaposi sarcoma; Meth: methilprednisolone; MMF: mycophenolate mofetil; MoAb: monoclonal antibody; Mo: month; Mos: months; NA: not available; NP: not performed; NS: not specified; PEL: primary effusion lymphoma; Rapa: rapamycin; RT: radiotherapy; TBI: total body irradiation; TC: tacrolimus; THA: thalidomide; TP: transplant; VCR: vincristine;
Patients with PT-PEL were aged between 29 and 72 years, with an average age of 54.9 years. Patients in their fourth, fifth and sixth decade of life were the most commonly affected. All PT-PEL occurred in males. In 7/13 cases ethnicity was reported (2 Haitian; 2 African; 2 Italian; 1 Chinese). In most cases (12/13) PEL developed after solid organ transplant (SOT) and only in one patient the disease presented after allogenic stem cell transplantation (ASCT) [7]. In 6/12 post-SOT cases, PEL occurred after kidney transplant [4, 5, 8, 10, 11]; in 3/12 cases, after cardiac transplant[2, 3, 12]; in 2/12, after liver transplant [6, 9]; in one case, after small bowel transplant [13]. The time from transplant to PEL diagnosis was between 5 to 340 months, with a median of 97.6 months.
Serological status and possible sources of HHV8 infection
Patients were HIV-negative in the majority of cases with known serological status (11/12), only one PT-PEL occurred in an HIV-positive patient [11]. HHV8 serology was reported in 6/13 cases. Two/6 patients, both from endemic regions, were pre-transplant HHV8-seropositive [4]. Two/6 patients (one of unknown ethnicity and the other from an HHV8 endemic area) resulted HHV8-negative at pre-transplant serological screening [6, 13]. In one patient from a non-endemic area, pre-transplant HHV8 serological status was not available and the patient resulted HHV8- seropositive at PEL diagnosis [8]. One patient, from an endemic area, was pre-transplant HHV8-negative and resulted HHV8-positive after transplant [12]. In the last patient, a remote history of polysubstance abuse was reported.
Immunosuppressive treatment following transplantation
At time of PEL diagnosis, all patients were receiving prolonged immunosuppressive treatment following transplantation. Azathioprine, cyclosporine and steroid in combination were used in 3/11 cases with known immunosuppressive treatment [2, 3, 5]. Tacrolimus was administered in 6/11 cases as follows: tacrolimus alone for 119 months after liver transplant and changed to rapamycin one month prior to PEL diagnosis (1/6) [9]; tacrolimus in combination with mycophenolate mofetil (1/6) [6], prednisone (1/6) [12], anti-CD52 antibody (1/6) [13], Highly Active Anti-Retroviral Therapy (HAART) (1/6) [11] or mycophenolate mofetil plus prednisone (1/6) [4]. In the last case, tacrolimus was changed to rapamycin for KS progression. In 1/11 cases cyclosporine was used associated with mycophenolate mofetil, prednisone and anti-CD25 antibody; then cyclosporine was converted to rapamycin for renal graft function impairment, 40 months before PEL diagnosis [4]. In the case occurring after ASCT, the patient had received myeloablative conditioning with cyclophosphamide and total body irradiation, followed by cyclosporine, steroid and thalidomide for graft versus host disease (GVHD) [7].
PEL clinical presentation
PT-PEL presented as serous effusions in body cavities in 10/13 cases (pleural effusion: 5/10 [2, 4, 5, 9, 12]; peritoneal effusion: 2/10 [3, 10]; pleural and peritoneal effusions: 2/10 [7, 8]; pericardial effusion: 1/10 [4]). In 1/13 cases, PT-PEL presented as pleural effusions associated with multiple organ involvement [11]. Two/13 cases were considered to be the extracavitary variant of PEL, as the patients had solid masses without any involvement of body cavities [6, 13]; in one of these cases, the lymphoma involved lungs, pleura, heart, intercostal muscles, Gerota fascia and omentum [6] ; in the other case, the disease presented as multiple gastric and duodenal polyps [13]. Bone marrow biopsy was positive in 2/4 cases evaluated [3, 12]; in one of these 2 cases bone marrow involvement was identified only at molecular level, being present a clonal neoplastic population [3].
Malignancies other than PEL
In 4/13 cases, KS occurred [2, 4, 11, 12]. In 2/4 cases, KS preceded PEL, developing 5 months after transplant [2, 4] and in one of these, KS initially progressed despite chemotherapy and reduction of immunosuppressive treatment (mycophenolate mofetil stopping and tacrolimus plus prednisone reduction); then KS partial remission was obtained with rapamycin administration and tacrolimus stopping [4]. In 1/4 cases, KS was discovered at post-mortem examination [11], whereas in 1/4 cases, KS occurred before transplant and was successfully treated with radiotherapy, but it recurred at PEL diagnosis [12]. In the case reported by Christenson, the patient developed squamous cell carcinoma of head and neck and was treated with surgery plus chemotherapy and radiotherapy [9].
Microscopic and immunohistochemical findings
PT-PEL was mostly diagnosed on the basis of cytological smears and cell block sections of effusion fluid. The cells were large, often pleomorphic, with prominent nucleoli and abundant basophilic cytoplasm occasionally showing vacuoles. The cells resembled immunoblasts, plasmablasts or anaplastic cells sometimes with Reed-Sternberg-like features. In the case by Cain et al [11], in which pleural effusions were associated with multi-organ involvement, histology revealed a peculiar intravascular pattern of growth. The lymphoma cells usually expressed CD45, markers of lymphocyte activation (CD30, CD38, EMA, HLA-DR) and markers of plasma cell differentiation (CD138, MUM1/IRF4). B-cell (CD19, CD20, CD79α) and T-cell (CD3, CD4, CD8) markers were usually absent. Aberrant CD3 positivity, in absence of other T-cell marker expression, was observed in the case by Kalogeraki et al [10]. The extracavitary-variant of PEL may be slightly different from classic PEL, being more often positive for some B-cell markers and negative for CD45/LCA. However, both cases of extracavitary PT-PEL were found to be negative for B-cell markers [6, 13]. PEL diagnosis requires the detection of HHV8 in the neoplastic cells. The standard assay to demonstrate viral infection is usually immunohistochemistry, detecting expression of HHV8-encoded latency-associated nuclear antigen 1 (LANA-1) protein. Epstein-Barr virus (EBV) infection was found by in situ hybridization for EBV-encoded small RNA (EBER) only in 2/7 cases evaluated [11, 13], one of which occurred in an HIV-positive individual [11]. Immunohistochemical assay of EBV latent membrane protein 1 (LMP1) was negative in 5/5 tested cases [2, 6, 8, 10, 12].
Molecular data
Polymerase chain reaction (PCR) demonstrated the presence of HHV8 genome in 7/7 evaluated cases [2, 3, 4, 5, 6, 7], two of which were tested by immunohistochemistry and found to be HHV8-LANA-1 positive [4]. EBV was identified by PCR in 2/4 cases, in which EBER was not tested [3, 5]. Clonal immunoglobulin heavy chain (IGH) gene rearrangement was identified in 5/7 cases evaluated [2, 3, 4, 8, 10] and in one of these, clonal immunoglobulin light chain (IGL) gene rearrangement was also identified [8]. In 1/7 cases, IGH gene rearrangement was negative [4] and in 1/7 cases, the result was not conclusive for poor DNA quality [11]. T-cell receptor (TCR) gene rearrangement was identified in 1/4 cases tested, the case by Kalogeraki et al [10] in which aberrant CD3 immunohistochemical expression was observed; TCR gene rearrangement was negative in 2/4 cases [4] and in 1/4, TCR result was not available for poor DNA quality [11]. Dotti et al identified the presence of 11q23 deletion, whereas BCL2/IGH translocation as well as BCL6, c-MYC and ALL-1 rearrangements were absent [3].
Treatment and outcome
In 7/13 cases, different chemotherapeutic schemes were performed (1/7: CHOP (cyclophosphamide, doxorubicin, prednisone, vincristine) [10]; 1/7: CHOP plus bleomycin [4]; 1/7: CHOP plus bleomycin and ifofosfamide plus etoposide [2] ; 1/7: cyclophosphamide plus vincristine plus prednisone [5]; 1/7: endoxan plus farmorubicin plus oncovin plus prezolon [8]; 1/7: intrapleural cidofovir, then, due to citofovir intolerance, bortezomib plus doxorubicin [9]; 1/7: cyclophosphamide plus vincristine plus brentuximab [12]. In 1/13 cases, only antiviral treatment with cidofovir was used [4]. Changes in the immunosuppressive treatment were performed at PEL diagnosis in 4/13 cases as follows: 1/4: tacrolimus was changed to sirolimus (rapamycin) resulting in undetectable HHV8 DNA blood level [12]; 1/4: cyclosporine reduction [2]; 1/4: cyclosporine reduction plus azathioprine stopping [3]; 1/4: cyclosporine and azathioprine stopping plus introduction of rapamycin [5]. In 1/13 cases, tacrolimus was changed to rapamycin due to altered renal function, 1 month prior PEL diagnosis and then rapamycin was continued [9]. Eleven/12 patients with available follow-up died from 2 weeks to 14 months from PEL diagnosis. In the case by Kugasia et al, death occurred 14 months after PEL diagnosis and it was unrelated to lymphoma [12]. Only 1/12 was alive at 10 months from PEL diagnosis, undergoing CHOP regimen [10].
Differential diagnosis
The main differential diagnoses for PEL include a spectrum of HHV8-associated lymphoproliferative disorders such as HHV8-positive multicentric Castleman disease (MCD) [1], HHV8-positive diffuse large B-cell lymphoma, not otherwise specified (HHV8-positive DLBCL, NOS) [1] and germinotropic lymphoproliferative disorder (GLPD) [1, 14]. Diffuse large B-cell lymphoma associated with chronic inflammation (DLBCL-CI) and HHV8-negative effusion-based lymphoma (EBL) need also to be considered in the differential diagnosis. The main differential diagnoses are summarized in Table 2.
Table 2
Main differential diagnoses
| PEL | HHV8 + MCD | HHV8 + DLBCL | GLPD | DBLCL-CI | HHV8-negative EBL | PBL |
Immunodeficiency | Usually present | Mostly present | Mostly present | Absent | Local immunodeficiency from longstanding chronic inflammation in a restricted space | Absent | Mostly present (HIV-related or due to age, transplant, autoimmune diseases or iatrogenic) |
HIV serology | + (- in elderly and EBV-negative cases) | + (90% of cases) | + (almost always) | - (rarely +) | - | - | + (often) |
Age/Sex/ Outcome | Adults, mainly males (HIV-negative pts are older) Unfavorable | Adults; HIV + pts mainly males Unfavorable | Adults Unfavorable | Adults Often favorable | Adults Unfavorable | Pts older than PEL pts Unfavorable | Adults (commonly) Unfavorable |
Clinical presentation | Effusion (classic PEL). Extra-nodal sites (often) and lymph nodes in extracavitary PEL. | Multiple lymphadenopathy, splenomegaly, KS, systemic symptoms | Systemic disease (nodal and extranodal sites, spleen, BM) | Lymphadenopathy (usually isolated) | Tumor mass involving body cavities or narrow spaces | Effusion (without detectable tumor masses as classic PEL) | Extranodal sites; rarely lymph nodes |
Association with MCD | rare | + | frequent | - | - | - | - |
Histology | PB/IB generally in fluids | PB/IB (single or in small aggregates mostly in mantle and interfollicular zones) | PB/IB in sheets | PB/IB (single or in small clusters in GC) | IB/CB | IB/PB/anaplastic | PB/IB (diffuse pattern of growth) |
CD20 | - (can be + in extracavitary PEL) | +/- | +/- | - | + (- in cases with plasmacytic morphology) | Often + | - or weakly + in a minority of cells |
PAX5 | - (can be + in extracavitary PEL) | - | - | - | + | Often + | - or weakly + in a minority of cells |
CD79α | - (can be + in extracavitary PEL) | -/+ | - | - | + (- in cases with plasmacytic morphology) | Often + | + in about 40% of cases |
MUM1/IRF4 | + | + | + | + (often) | + in cases with plasmacytic morphology | Often + | + |
CD10 | - | - | - | - | - | - | - (rarely +) |
BCL6 | - | - | - | - | - | - | - |
BCL2 | - | - | - | - | - | + | - |
CD38 | + | -/+ | -/+ | +/- | - | - | + |
CD138 | + | - | - | - | + in cases with plasmacytic morphology | -/+ | + |
CD30 | + | - | - (rarely +) | +/- | Often + | -/+ | + |
CD15 | - | - | - | - | - | - | - |
EMA | Often + | - | - | - | - | - | + |
T cell markers | Occasionally + (especially in extracavitary PEL) | - | - | Occasionally + | Occasionally + | - | Occasionally + |
Light chain restriction | Usually absent | + cIgM lambda | + cIgM lambda | + kappa or lambda | Often + | Often + | + (often IgG kappa or lambda) |
HHV8 | + | + | + | + | - | - | - |
EBV (by LMP1) | LMP1- | LMP1- | LMP1- | LMP1- (EBNA2-, BZLF-1-, type I EBV latency) | LMP1+ (EBNA1+, EBNA2+, type III EBV latency) | - | LMP1 - |
EBV (by EBER) | + (- in HIV-negative elderly pts and in transplanted pts) | - | - | + | + | - | + in 60–75% of cases |
Clonality | Monoclonal (IG genes hypermutated). Rare MYC, BCL2, BCL6 | polyclonal | Monoclonal (IgG genes unmutated) | Polyclonal or oligoclonal (rarely monoclonal) | Monoclonal (IG genes hypermutated) | Monoclonal (IG genes hypermutated) Frequent MYC, BCL2, BCL6 rearrangements | Monoclonal |
Legends: BM: bone marrow; CB: centroblasts; DLBCL-CI: diffuse large B-cell lymphoma associated with chronic inflammation; EBV: Epstein Barr-virus; EBER: in situ hybridization for EBV-encoded RNA; GLPD: germinotropic lymphoproliferative disorder; HD-like: Hodgkin-like; HHV8 + MCD: HHV8-positive multicentric Castleman disease; HHV8 + DLBCL: HHV8-positive diffuse large B-cell lymphoma; HHV8- negative EBL: HHV8-negative effusion based lymphoma; IB: immunoblasts; LMP1: Latent membrane protein; KS: kaposi sarcoma; PB: plasmablasts; PBL: plasmablastic lymphoma; PEL: primary effusion lymphoma; pts: patients |
HHV8-positive MCD commonly affects HIV-positive patients and rarely HIV-negative individuals from HHV8-endemic regions [1]. In the setting of SOT, mainly kidney, liver and heart transplantation, 11 cases of MCD have been reported so far [15]. HHV8-positive MCD shows systemic symptoms, multiple lymphadenopathy, cytopenia, splenomegaly, hypoalbuminemia, hypergammaglobulinemia, elevated serum levels of inflammatory markers such as C-reactive protein and interleukin 6 (IL-6) [1]. The disease usually shows an unfavorable outcome. The key histological features are regressed and hyalinized germinal centers (GCs) with prominent penetrating venules and interfollicular polytypic plasma cells [1]. Plasmablasts, isolated or in small aggregates, are seen within the mantle zone and interfollicular region. Plasmablasts, which are always IgM lambda positive, are commonly negative for B-cell markers (CD20, PAX5, CD79α) and CD138, and positive for CD38 and MUM1IRF4 [1]. MCD is usually EBV-negative and strongly associated with HHV8 infection, especially in HIV-positive cases. Despite monoclonal immunoglobulin, MCD often lacks monoclonal IGH gene rearrangement. In MCD, plasmablasts are scattered or in small clusters and, in a small number of cases, they may give rise to HHV8-positive DLBCL, NOS.
This aggressive lymphoma usually arises in HIV-positive individuals in the setting of HHV8-positive MCD and rarely de novo [1]. Recently two cases of HHV8-positive, DLBCL, NOS have been reported in renal transplant recipients [16]. Unlike PEL commonly involving body cavities without forming a mass, HHV8-positive DLBCL, NOS usually affects lymph nodes, spleen and liver; extranodal sites and bone marrow are often involved [1]. The architecture is totally effaced by sheets of plasmablasts. By definition, the neoplastic cells are HHV8-positive and EBV-negative [1]. The cells show the same MCD phenotype such as IgM lambda, MUM1/IRF4 and CD38 positivity and absence or weak expression of B-cell antigens, CD30 and CD138 [1]. Differentiating PEL, in its extracavitary variant, from HHV8-positive DLBCL, NOS can be difficult. PEL is often positive for CD138, EMA and CD30, in absence of cytoplasmic immunoglobulin. Unlike HHV8-positive DLBCL, NOS, PEL often shows HHV8 and EBV co-infection, especially in HIV- positive individuals. However, EBV infection is rarely identified in PEL affecting elderly as well as transplanted individuals. As mentioned above, the majority of PT-PEL, in which EBER was evaluated, were negative. This makes very tricky the differential diagnosis between PEL, in its extracavitary variant, and HHV8-positive DLBCL, NOS.
GLPD is a recent entity strictly linked to HHV8 infection, usually with an indolent behavior [1, 14]. It affects mainly immunocompetent individuals, with only rare cases described in HIV-positive patients [14]. GLPD has not been described in transplanted individuals. Patients are generally asymptomatic with localized lymphadenopathy. Aggregates of plasmablasts generally involving GCs of lymphoid follicles and co-infected by HHV8 and EBV are the key features [1, 14]. Plasmablasts are usually negative for B-cell markers (CD20, CD79α, PAX5) and CD138, with variable positivity for MUM1/IRF4, CD38 and CD30. An aberrant expression for T cell markers (CD3) can be present [17]. Plasmablasts often show monotypic kappa or lambda light chains, unlike MCD which is always IgM lambda positive. Despite monotypic immunoglobulin expression by plasmablasts, GLPD shows mainly a polyclonal pattern of IG gene rearrangement and rarely an oligoclonal or monoclonal pattern.
PEL, especially in its solid-form, can be misinterpreted as anaplastic large cell lymphoma (ALCL), due to the possible aberrant expression of T-cell markers together with CD30 positivity, however ALCL is always HHV8 negative. It is worth mentioning that in the case of PT-PEL positive for TCR gene rearrangement, a T-cell lymphoma was excluded due to HHV8 positivity [10].
DLBCL-CI is a mass-forming, EBV-driven aggressive neoplasm arising in the context of persistent chronic inflammation generally involving body cavities or narrow spaces [1]. The prototype of this category is pyothorax-associated lymphoma (PAL) which is a DLBCL occurring in patients who have undergone artificial pneumothorax as a therapy for tuberculosis and subsequently develop chronic pyothorax [1].
Unlike PEL classically not mass forming, in PAL patients present with a mass involving the pleura. The cells have a centroblastic or immunoblastic morphology and generally express B cell markers (CD20, CD79α); T-cell markers may be aberrantly expressed. CD30 can be positive [1]. A subset of cases with a plasmacytic morphology, lacking B cell markers and positive for plasma cell markers (MUM1/IRF4 and CD138) may be more difficult to differentiate from PEL. However, unlike PEL, DLBCL-CI is always HHV8 negative and EBV positive, with type III EBV latency pattern (positivity for LMP1 and EBNA2).
Recently another EBV-positive and HHV8-negative entity has been included among DLBCL-CI, but renamed fibrin-associated diffuse large B-cell lymphoma (FA-DLBCL), because it develops within fibrinous material usually in the context of pseudocysts, cardiac myxoma, valve prosthesis, fibrin thrombus, synthetic tube graft, hydrocele, metallic implants and chronic subdural hematoma [1, 18, 19]. Differently from PAL which is mass-forming and follows an aggressive course, FA-DLBCL does not form masses and mostly has an indolent behavior often with the only surgery.
HHV8-negative EBL is a group of large B-cell lymphoma presenting as effusion without detectable tumor masses, a feature in common with typical PEL. Compared with PEL, in HHV8-negative EBL, patients are often older, HIV-negative and non-immunocompromised [20]. Some cases may be associated with a fluid overload status and hepatitis C infection. Morphologically the neoplastic cells are large with immunoblastic, plasmablastic or anaplastic fetaures, an overlapping morphology with PEL [20]. Unlike PEL showing a plasmablastic phenotype and lacking B-cell markers, the tumor cells of HHV8-negative EBL frequently express B-cell markers and less frequently CD138 and CD30. HHV8 is absent by definition. EBER is more frequently positive in classic PEL than in HHV8-negative EBL [20].
Focusing on HHV8 infection in the transplantation setting
HHV8 is a gamma herpesvirus related to EBV. HHV8 was initially identified in KS and named KS-herpesvirus (KSHV) [21]. Later, HHV8 was identified to be the causative agent of MCD [22] and PEL[23]. Most HHV8-associated diseases occur in immunocompromised individuals, with the exception of GLPD [1, 14]. HHV8 is not ubiquitous in the worldwide population. There are geographic areas such as sub-Saharan Africa, Latin America, Carabbean, Mediterranean and Middle Eastern countries where HHV8 infection is endemic and there is a known high incidence of classic/endemic KS [24]. Transmission of virus occurs through saliva, but it may be transmitted sexually, vertically through breast milk, by intravenous drug use, blood transfusion and through transplant [25]. As EBV, HHV8 may infect lymphoid cells and other cell types like endothelial cells and persist lifelong in a latent form [25]. When the immune control decreases, HHV8 may reactivate the lytic replicative cycle producing viremia. In post-transplant patients, iatrogenic immunosuppression may be the cause of HHV8 reactivation, leading to uncontrolled expansion of latently infected endothelial cells or mature post-germinal center B cells [25]. HHV8-related diseases occurring in the setting of transplantation may be the result of reactivation of a pre-existing HHV8 infection in the recipient host or of HHV8 transmission from HHV8-seropositive donors. The risk to develop post-transplant HHV8-related diseases depends on the ethnic origin of both the donor and the recipient. Given the lack of standardization and variable sensitivity and specificity, HHV8 serologic testing is not routinely included in pre-transplant screening [25]. Despite being the seroconversion rate among seronegative SOT transplant recipients from seropositive donors quite high (30% by indirect immunofluorescence), the development of HHV8 viremia and HHV8-driven diseases is much less frequent. For this reason, screening SOT recipients and donors for HHV8 to assess the risk of post-transplant HHV8-related diseases is not used in routine practice [25].