INTRODUCTION

Primary effusion lymphoma (PEL) is a rare extranodal non-Hodgkin lymphoma of large B-cells that typically develop as a liquid-phase tumor in body cavities lined by serous membranes, without solid tumor formation. First identified in human immunodeficiency virus (HIV)-associated lymphomas in 1995, Kaposi sarcoma-associated human herpesvirus 8 (HHV8) sequences are central to PEL pathogenesis, as outlined in the World Health Organization classification. PEL accounts for 0.1% to 4% of HIV-related lymphomas, with limited data on its occurrence in HIV-negative, immunocompromised individuals. Cancer registry data, such as the surveillance, epidemiology and end result database (SEER) database, predominantly document PEL in HIV-positive populations, with HIV-negative cases mainly represented in isolated reports. Clinically, PEL presentation depends on the site of effusions, with pleural effusions causing dyspnea and pericardial effusions leading to hypotension due to cardiac tamponade. Systemic symptoms, including weight loss, fever, and night sweats, as well as lymphadenopathy and splenomegaly due to B-cell proliferation, are also common.[1]

PEL is diagnosed by cytology workup of the aspirated material from the effusion.[2] In this report, we discuss the clinical manifestation, laboratory workup, imaging studies, cytological features, and management plan of a rare case of PEL.

CASE REPORT

An 84-year-old male with a history of testicular cancer presented due to worsening dyspnea with SpO2 of 88% on exertion, negative for orthopnea, claudication, palpitations, fever, or weight loss. Decreased breath sounds, dull percussion over the left chest, and bilateral lower extremity edema were noted. Chest X-ray demonstrated near-complete opacification of the left hemithorax and associated atelectasis as shown in Figure 1.

Figure 1: Left pleural effusion with re-expansion pulmonary edema. (a) Anterioposterior view chest X-ray demonstrates a large left pleural effusion resulting in near-complete opacification of the left hemithorax, (b) non-contrast chest CT scan following thoracocentesis demonstrates re-accumulation of a small left pleural effusion and development of re-expansion pulmonary edema. CT: Computed tomography.

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2850 mL of serosanguinous fluid was drained from the left pleural cavity. Post-thoracentesis computed tomography (CT) image is shown in Figure 1. Pleural fluid analysis showed red blood cell count of 601,000 with 28% neutrophils, 27% lymphocytes, 23% monocytes, 3% eosinophils, 10% macrophages, and 9% mesothelial cells. The albumin was 2.5 g/dL, protein 5.5 g/dL, glucose 40 mg/dL, lactate dehydrogenase >3325 IU/L, and triglyceride 19 mg/dL with pH of 7.5.

Microbiology workup showed no growth. The flow cytometry of the pleural fluid had validity of 90%, 10 × 106 cells were recovered which revealed a population of large cells with moderate to dim cluster of differentiation [CD]45 expression and bright CD38 positivity, lacking expression of CD10, CD19, CD20, surface immunoglobulin light chains (kappa and lambda), and T-lineage markers (CD2, CD3, CD4, CD5, CD7, and CD8). This demonstrated 32% small T lymphocytes (CD4:CD8 = 4.0:1), 9.0% small B lymphocytes with no surface light chain expression, 3.2% granulocytes, 1.8% natural killer cells, and 16% large cells of uncertain phenotype as shown in Figure 2.

Figure 2: Flow cytometry evaluation of pleural fluid. (a) The flow cytometry detected a population of large cells (b) with expression of CD45 (moderate/dim), (c) negativity of CD10, CD20, (d) positivity of CD 38 (bright) and (e) having no expression of surface kappa and lambda, (f) CD19, (g) CD3, CD2, (h) CD7, (i) CD5, (j) CD4 and CD8. CD: Cluster of differentiation.

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50 mL of blood fluid was received in ThinPrep CytoLyt solution (ASY-15207, Hologic Inc., Massachusetts, U.S.A.), and the entire fluid was centrifuged at 2200 revolutions per minute (RPM) for 6 min, using IEC Centra CL3 (Model # 37500984, Avantik, New Jersey, U.S.A.). The sediment was wrapped in Leica Surgipath BioWraps and placed in 10% formalin, then transferred to histology. The tube was then filled with 20 mL of ThinPrep PreservCyt solution. The tube was vortexed at 3000 RPM for 10–15 min with Digital Vortex Mixer (Model # 945415, Fisher Scientific, Pennsylvania, USA). The solution was then transferred back to ThinPrep container. After at least 10 min at room temperature, the cup was placed in Hologic ThinPrep 2000 to make a thin prep slide. The slide was stained along non-gynecological (non-GYN) pap stain protocol at Leica Autostainer (Model # 5560, Avantik, New Jersey, USA). Pleural cytology demonstrated a few atypical lymphocytes admixed with benign mesothelial cells in ThinPrep and cell block. The immunostains were performed on the cell block which was positive for CD20 and CD45 and negative for pancytokeratin and S100 and was signed out as atypia as shown in Figure 3.

Figure 3: Cytological evaluation of pleural fluid. ThinPrep cytology shows (a) atypical lymphocytes, high NC ratio, cherry red nucleoli, and multinucleation with (b) reactive mesothelial cells having binucleation. (c) The cell block shows large pleomorphic atypical neoplastic cells with amphophilic cytoplasm, which are negative for (d) S100 immunostain rules out melanoma, (e) AE1/AE3 rules out carcinoma and positive for (f) CD45 indicates the lymphocytes as origin of neoplastic cells and (g) focally positive for CD20 indicating that neoplastic cells are of B cell origin. Scale bars for (a and b): 40 µm (400 b) magnification, scale bars for (c-g): 100 µm (200 ×) magnification. CD: Cluster of differentiation, NC: Nuclear to cytoplasmic ratio, µm: Micrometer.

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The patient developed recurrent pleural fluid in 2 weeks. 3 L of bloody fluid was drained from the left pleural cavity. Microbiology culture workup was negative. The concurrent pleural biopsy showed acute fibrinous and organizing pleuritis. ThinPrep revealed large atypical neoplastic cells with prominent nucleoli. The cell block showed pleomorphic neoplastic cells with apoptotic debris and characterized by irregular nuclear membranes, coarse chromatin, prominent nucleoli, amphophilic cytoplasm, and multinucleated and Reed–Sternberg-like cells as shown in Figure 4.

Figure 4: Cell block and IHC evaluation of pleural fluid. (a) Cell block showed pleomorphic neoplastic cells with apoptotic debris, characterized by uneven nuclear membranes, coarse chromatin, amphophilic cytoplasm, mitotic figures (blue arrows show mitotic figures) and (b) Reed–Sternberg-like cell (green arrow). (c) Reactive histiocytes are stained positive with CD68 and (d) neoplastic cells are negative for CD3 with surrounding positivity for T lymphocytes (black arrow point toward neoplastic cells) and stain positive for (e) CD30 and (f) HHV8. Scale bars: 100 µm (200 × magnification). CD: Cluster of differentiation, HHV8: Human herpesvirus 8, IHC: Immunohistochemical stain, µm: Micrometer.

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Differential diagnoses include poorly differentiated carcinoma, large cell lymphoma, and melanoma. CD45 and CD20 highlight the malignant cells. Negative AE1/AE3 and S100 excluded the carcinoma and melanoma, respectively, as shown in Figure 4. The immunostaining pattern, along with clinical history and radiology, supports the diagnosis of PEL as mentioned in Table 1.

Table 1: IHC panel, their result, antibody number along with manufacturer information.

Immunostain Result Antibody number Manufacturer information AE1/AE3 Negative 760–2595 Roche/Ventana CD45, LCA Diffusely positive 760–2505 Roche/Ventana CD20 Focally positive 760–2531 Roche/Ventana CD3 Patchy positive 790–4341 Roche/Ventana MOC-31 Negative 790–4561 Roche/Ventana S-100 Negative 760–2523 Roche/Ventana CD68 Focally positive 790–2931 Roche/Ventana CD30 Positive 790–4858 Roche/Ventana CAM5.2 Negative 790–4555 Roche/Ventana CD138 Negative 760–4248 Cell Marque HHV8 Positive N/A N/A ALK1 Negative 790–2819 Roche/Ventana

A staging positron emission tomography/CT (PET/CT, Siemens Biograph mCT Flow motion S64 4R, year 2021, with software PETSYNGO VG80C) scan revealed a reduction in the size of a pleural effusion on the left side, with no notable uptake of fluorodeoxyglucose. Ground-glass opacities in the lower left lung improved, suggesting resolution of re-expansion pulmonary edema noted on the prior non-contrast CT. Post-procedure imaging revealed no nodal disease or radiotracer uptake in the spleen, with physiologic uptake observed in the colon and urinary tracts. The PET/CT scan is shown in Figure 5.

Figure 5: PET/CT scan evaluation. PET maximum intensity projection images from PET/CT demonstrate no significant FDG activity in the left lung. There is an absence of uptake in the lymph nodes and spleen. FDG: Fluorodeoxyglucose, PET/CT: Positron emission tomography/computed tomography.

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Given his age, the patient started treatment with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone at reduced doses (R-miniCHOP). His interim PET/CT scan after 3 cycles of treatment showed a continued decrease in the size of the left pleural effusion and low-grade metabolic activity of the pleura without focal abnormalities (Deauville 2). He completed 6 cycles of treatment without experiencing any toxicities. The patient’s only site of disease was the pleural space. Since the pleural effusions resolved, the patient had no further evidence of disease and was asymptomatic.

DISCUSSION

PEL is primarily observed in HIV-positive populations, with a median age of 45-55 years and a male predominance. In contrast, the median age for HIV-negative PEL patients is 73.[3] HIV-negative cases are often associated with hepatitis B or C-related cirrhosis, prior organ transplantation, or immunosuppressive therapy.[2] Few cases of PEL have been reported without an underlying immunocompromised condition.[4] In our case, the patient was a male in his 80s with a remote history of testicular cancer but no active cancer other than the PEL.

PEL is primarily driven by Kaposi’s sarcoma-associated herpesvirus (HHV8), with all tumor cells harboring episomal viral DNA. A subset of these cells undergoes lytic replication. Key viral proteins implicated in PEL pathogenesis include latency-associated nuclear antigen (LANA), vCyclin, vFLIP, vIRF3, and kaposin B. LANA interacts with tumor suppressors (p53, RB1, and GSK3B), disrupting their regulatory functions. vCyclin, a homolog of cyclin D, modulates cell cycle progression, while vFLIP constitutively activates NF-κB, promoting cytokine expression and anti-apoptotic signaling crucial for cell survival. vIRF3, structurally related to IRF4, negatively regulates interferon responses, impacting B-cell differentiation. Kaposin B enhances cytokine stability, notably interleukin-6 and granulocyte-macrophage colony-stimulating factor, contributing to the pro-inflammatory microenvironment that supports PEL pathogenesis.[3,5]

PEL cells exhibit pleomorphism, ranging from immunoblasts/plasmablasts to larger anaplastic cells. Nuclei are pleomorphic with prominent nucleoli, and the cytoplasm is abundant, basophilic, and often contains vacuoles as is seen in our case. These features complicate diagnosis, necessitating immunostaining to differentiate PEL from poorly differentiated carcinomas, melanomas, and other large cell lymphomas.[3-5]

Immunophenotypical studies indicate that neoplastic cells display a “null” phenotype. They express CD45 markers, whereas B cell markers such as CD79a, CD19, CD20, PAX5, and surface immunoglobulins are typically negative but with focal CD20 positivity in HIV HIV-negative population.[2,3] T cell markers exhibit variable expression.[6,7] Plasma cell markers are commonly positive.[1,3,4,7] In our case, the flow cytometry reported that the neoplastic cells neither express any immunoglobulin markers nor B or T lymphocyte markers.

Given the rarity of PEL, there is no established standard treatment for the disease. PEL is considered resistant to chemotherapy, and commonly used treatment regimens include high doses of chemoimmunotherapy. The National Comprehensive Cancer Network guidelines recommend rituximab, etoposide, cyclophosphamide, doxorubicin, vincristine, and prednisone as first-line therapy. R-CHOP is another recommended regimen.[3] In our case, the patient was not eligible for intensive treatment due to his age and received an attenuated version of R-CHOP (R-miniCHOP). The same drugs are used in both R-miniCHOP and other anthracycline-based regimens such as DA-EPOCH-R. These regimens have been tested in this disease and shown to have activity in case reports.[1] A complete response to treatment was achieved, despite the poor prognosis associated with this disease.

A recent study found improved survival in treated patients, with notable benefits in the HIV-positive cohort, where chemotherapy significantly improved survival compared to no treatment. In contrast, no survival advantage was observed with chemotherapy and no chemotherapy in the HIV-negative cohort. The patient in this case underwent chemotherapy and achieved full recovery, with post-treatment PET scans showing no evidence of disease.[8]

SUMMARY

In summary, we reported an unusual case of PEL in an elderly patient with no known immunosuppression status and HIV negative. Cytology of pleural effusion provides diagnostic neoplastic cells and is confirmed by appropriate immunostains. This case uniquely reported a primary PEL patient with complete remission after attenuated R-miniCHOP in our patient. PEL remains a rare entity and is a diagnosis of exclusion. We emphasize that the cytology of pleural fluid, along with clinical, radiological, and flow cytometry correlation, is a diagnostically accurate method for the initial diagnosis of PEL.

AVAILABILITY OF DATA AND MATERIALS

The data and materials that support the findings of this study are available from the corresponding author upon reasonable request.

ABBREVIATIONS

ALK1: Anaplastic lymphoma kinase 1

CD: Cluster of differentiation

FDG: Fluorodeoxyglucose

GM-CSF: Granulocyte-macrophage colony-stimulating factor

HHV8: Human herpesvirus 8

HIV: Human immunodeficiency virus

IHC: Immunohistochemical

IL6: Interleukin 6

KSHV: Kaposi’s sarcoma-associated herpesvirus

LANA: Latency-associated nuclear antigen

LDH: Lactate dehydrogenase

NC: Nuclear-to-cytoplasmic ratio

PEL: Primary effusion lymphoma

PET/CT: Positron emission tomography/computed tomography

R-EPOCH: Rituximab, etoposide, cyclophosphamide, doxorubicin, vincristine, and prednisone

R-miniCHOP: Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone at reduced doses µm: Micrometer

AUTHOR CONTRIBUTIONS

MI: Coordinated with the clinical, radiology, and hematopathology teams to collect relevant information, gathered images for cytology, immunohistochemistry (IHC), and tissue block slides, and was responsible for drafting the manuscript. JHZ: Designed the overall study, oversaw coordination among clinical, radiological, and hematopathological teams, and supervised the entire study process. JV: Contributed clinical and management-related information and participated in manuscript writing. PS provided radiological images and contributed to the writing of the manuscript. XYH: Provided flow cytometry images along with their interpretation. All authors have been involved in revising it critically for important intellectual content. All authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work, ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors meet the authorship status of ICMJE.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

The institutional review board of New York University Grossman Long Island School of Medicine approval is not required for the single case report study (Reference number: i24-01032 and s24-01032). The patient has provided consent to publish his clinical and other related information. The study complies with the Helsinki Declaration.