Prognostic factors of methotrexate-associated lymphoproliferative disorders associated with rheumatoid arthritis and plausible application of biological agents

A case of methotrexate-related lymphoproliferative disease showing multiple liver lesions in a patient with rheumatoid arthritis

A 66-year-old woman with rheumatoid arthritis (RA) who had been receiving methotrexate (MTX) for 2 years presented with tarry stools. Contrast-enhanced computed tomography (CT) of the abdomen revealed irregular wall thickening in the ileocecal region and multiple low-contrast masses in both lobes of the liver. Lower gastrointestinal endoscopy revealed a type 2 tumor in the ileocecal region with a semi-peripheral ulcer. Histological examination of liver and colon biopsies showed other iatrogenic immunodeficiency-associated lymphoproliferative disorder (Oi-LPD), diffuse large B-cell lymphoma type, with positivity for Epstein-Barr virus DNA. After withdrawal of MTX, the LPD lesions disappeared and the patient achieved remission. We considered this to be a sporadic case of Oi-LPD, diffuse large B-cell lymphoma type, in the liver and colon due to treatment with MTX. There has been no previous report of this condition with simultaneous hepatic and colonic lesions, and the present case is thought to be highly informative in relation to the pathogenesis.

The incidence and prognosis of other iatrogenic immunodeficiency-associated lymphoproliferative disorders of the lung related to methotrexate: A retrospective study

BACKGROUND AND OBJECTIVE

Other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPD) are rare but well-known diseases that manifest during or after methotrexate (MTX) administration. Limited information is available on the clinical characteristics of OIIA-LPD of the lung because only a few cases have been reported. Thus, we aimed to assess the incidence and prognosis of patients with OIIA-LPD of the lung.

METHODS

Patients with OIIA-LPD of the lung treated at our institution between January 2008 and July 2020 were retrospectively analysed.

RESULTS

Among the 51 patients with OIIA-LPD, 16 (31.3%, 7 men, 9 women) had OIIA-LPD of the lung (median age, 69 [range, 63-82] years). Peripheral lesions were observed in 10 (62.5%), central lesions in two (12.5%), and both lesions in four (25.0%) patients. Nine of the 16 patients underwent bronchoscopic biopsy, seven were diagnosed (diagnostic yield, 77.8%) and, re-biopsy was performed in 2 patients. Eight (50.0%) patients had LPD and six (37.5%) had diffuse large B-cell lymphoma. In the 14 patients with confirmed treatment efficacy, the overall response rate to MTX withdrawal was 71.4%. However, chemotherapy was required in case of larger lesions (three patients). Death related to OIIA-LPD occurred in only one patient, and 11 of the 14 patients were alive during the study period (median follow-up time, 53.7 [range, 4.3-84.2] months).

CONCLUSION

The incidence of OIIA-LPD of the lung is 31.3% and higher than that reported previously. The treatment effect of MTX withdrawal seems to be sufficient; however, in some cases, chemotherapy may be required from the beginning.

Effect of Recent Antirheumatic Drug on Features of Rheumatoid Arthritis-Associated Lymphoproliferative Disorders

OBJECTIVE

In this study, we examine how advancements in novel antirheumatic drugs affect the clinicopathologic features of lymphoproliferative disorder (LPD) in patients with rheumatoid arthritis (RA).

METHODS

In this multicenter study across 53 hospitals in Japan, we characterized patients with RA who developed LPDs and visited the hospitals between January 1999 and March 2021. The statistical tools used included Fisher's exact test, the Mann-Whitney U-test, the log-rank test, logistic regression analysis, and Cox proportional hazards models.

RESULTS

Overall, 752 patients with RA-associated LPD (RA-LPD) and 770 with sporadic LPD were included in the study. We observed significant differences in the clinicopathologic features between patients with RA-LPD and those with sporadic LPD. Histopathological analysis revealed a high frequency of LPD-associated immunosuppressive conditions. Furthermore, patients with RA-LPD were evaluated based on the antirheumatic drugs administered. The methotrexate (MTX) plus tacrolimus and MTX plus tumor necrosis factor inhibitor (TNFi) groups had different affected site frequencies and histologic subtypes than the MTX-only group. Moreover, MTX and TNFi may synergistically affect susceptibility to Epstein-Barr virus infection. In case of antirheumatic drugs administered after LPD onset, tocilizumab (TCZ)-only therapy was associated with lower frequency of regrowth after spontaneous regression than other regimens.

CONCLUSION

Antirheumatic drugs administered before LPD onset may influence the clinicopathologic features of RA-LPD, with patterns changing over time. Furthermore, TCZ-only regimens are recommended after LPD onset.

The role of Epstein-Barr virus in autoimmune and autoinflammatory diseases

Epstein-Barr Virus (EBV), a dsDNA herpesvirus, is believed to play a significant role in exacerbating and potentially triggering autoimmune and autoinflammatory maladies. Around 90% of the world is infected with the virus, which establishes latency within lymphocytes. EBV is also known to cause infectious mononucleosis, a self-limited flu-like illness, in adolescents. EBV is often reactivated and it employs several mechanisms of evading the host immune system. It has also been implicated in inducing host immune dysfunction potentially resulting in exacerbation or triggering of inflammatory processes. EBV has therefore been linked to a number of autoimmune diseases, including systemic lupus erythematosus, multiple sclerosis, rheumatoid arthritis, and Sjögren's syndrome. The review examines the molecular mechanisms through which the virus alters host immune system components thus possibly resulting in autoimmune processes. Understanding the mechanisms underpinning EBV-associated autoimmunity is pivotal; however, the precise causal pathways remain elusive. Research on therapeutic agents and vaccines for EBV has been stagnant for a long number of years until recent advances shed light on potential therapeutic targets. The implications of EBV in autoimmunity underscore the importance of developing targeted therapeutic strategies and, potentially, vaccines to mitigate the autoimmune burden associated with this ubiquitous virus.

The first case of methotrexate-associated lymphoproliferative disorder in the sacrum: a case report

Methotrexate (MTX) is a drug used for treating rheumatoid arthritis. Recently, the reported incidence of methotrexate-associated lymphoproliferative disease (MTX-LPD) has increased, especially in Japan. Extranodal involvement is observed in half of MTX-LPD cases. However, only a few spinal lesions have been reported, with none in the sacrum. Additionally, Epstein-Barr virus (EBV) infection has also been implicated in the pathogenesis of MTX-LPD. Herein, we describe the case of a 74-year-old woman with MTX-LPD in the sacral spine who complained of severe back pain and nocturnal pain. Radiographs revealed a tumour on the right wing of the sacrum and a positive EBV immunoglobulin G antibody titre. MTX-LPD was suspected based on imaging findings and a history of MTX administration. A pathological examination was performed on the CT-guided biopsy specimen. The histopathological diagnosis was MTX-LPD, and MTX was discontinued. Three months after MTX administration ended, the tumour tended to shrink, and 1 year later, significant tumour shrinkage was observed. This experience suggests that MTX-LPD can be treated by discontinuing MTX administration. Therefore, early and accurate diagnosis is required, as is avoiding unnecessary treatment such as surgery. MTX-LPD should be considered, especially in spinal origin tumours in EBV-infected patients on MTX.

Methotrexate‑related other iatrogenic immunodeficiency‑associated lymphoproliferative disorder in the CNS and medication‑related osteonecrosis of the jaw occurring simultaneously: A case report

Methotrexate-related other iatrogenic immunodeficiency-associated lymphoproliferative disorder (MTX-OIIA-LPD) is prone to extranodal involvement but rarely involves the central nervous system (CNS). The present study reports a case of MTX-OIIA-LPD of the CNS discovered during medication-related osteonecrosis of the jaw (MRONJ) treatment in a 76-year-old woman with rheumatoid arthritis (RA). The chief complaint of the patient was bone exposure and pain in the right mandibular molar. The patient had been receiving MTX for RA and alendronate sodium hydrate for osteoporosis, followed by denosumab. Treatment was initiated based on a diagnosis of MRONJ. However, the patient experienced lightheadedness and floating dizziness afterwards. Examinations revealed scattered neoplastic lesions in the brain. The histopathological diagnosis was diffuse large B-cell lymphoma. A systemic search also revealed adrenal involvement. Since the patient was taking MTX, a diagnosis of MTX-OIIA-LPD was made and MTX was discontinued. Chemotherapeutic agents were administered since the central lesions became symptomatic. The MTX-OIIA-LPD lesions in the brain and adrenal glands completely resolved 8 months after onset. The physical condition of the patient improved, and the bone-exposed areas became epithelialized. Reports on MTX-LPD in the oral and maxillofacial region are few, which may delay its diagnosis. Therefore, biopsy of oral lesions in patients with MRONJ who are taking MTX and collaboration with related diagnostic departments, such as rheumatology and hematology, must be done to initiate the diagnosis and treatment of extraoral MTX-LPD.

FDG-PET/CT imaging parameters for predicting spontaneous regression of methotrexate-associated lymphoproliferative disorder in patients with rheumatoid arthritis

In this study, we investigated the usefulness of FDG-PET/CT for predicting spontaneous regression in methotrexate-associated lymphoproliferative disorder (MTX-LPD). Twenty patients with rheumatoid arthritis who were diagnosed with MTX-LPD were enrolled in the study. These patients were divided into those who showed spontaneous regression (SR group: ten patients) and those who received chemotherapy after discontinuation of MTX (CTx group: ten patients). Between-group differences in potential biomarkers were compared, including clinical markers at the onset of LPD [serum LDH and interleukin 2 receptor (sIL-2R)], change in absolute number of peripheral lymphocytes (ΔALC) over follow-up, and the FDG-PET/CT-derived parameters of maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), sum of the metabolic tumor volume (MTVsum), and sum of total lesion glycolysis (TLGsum). The levels of sIL-2R, MTVsum, and TLGsum were significantly lower in the SR group than in the CTx group. In addition, ΔALC was higher in the SR group. In conclusion, MTV and TLG values measured by FDG-PET/CT may be suitable for use as predictors of SR in patients with MTX-LPD.

Spontaneous regression of breast lymphoproliferative disorders after withdrawal of methotrexate in rheumatoid arthritis patients with Epstein–Barr virus infection: a case report and review of the literature

Background

Lymphoproliferative disorder (LPD) has been shown to occur after treatment with methotrexate (MTX). Currently, MTX-LPD has become widely recognized, but its mechanism and prognostic factors remain unclear.

Case presentation

We report the first case of Epstein–Barr virus (EBV)-associated MTX-LPD of the breast. A 63-year-old Asian woman with long-term rheumatoid arthritis presented to our facility with intermittent fever. A physical examination revealed a 3-cm lump in her left breast. She had been taking MTX for the past 15 years. Laboratory studies revealed slightly elevated levels of EBV-viral capsid antigen antibody immunoglobulin G and EBV nuclear antibody. Contrast-enhanced computer tomography revealed a mass in the left breast, a subcutaneous nodule in the abdomen, a mass in the left lung, and a nodule in the left retroperitoneum. The definitive diagnosis was consistent with MTX-LPD merging into an EBV-positive, diffuse large B-cell lymphoma. Six months following the withdrawal of MTX, the breast mass had markedly shrunk and the patient remained in good health for 1 year with no evidence of relapse of LPD.

Conclusion

MTX-LPD rarely occurs in the breast, and it is difficult to diagnose because there have only been six reported cases of breast MTX-LPD reported in the literature. EBV-positive MTX-LPD tends to regress spontaneously after MTX withdrawal, and our case also had similar results. It is important to make an appropriate diagnosis of MTX-LPD of the breast based on imaging and pathology to determine the appropriate treatment protocol for this rare disorder.

Primary Central Nervous System T-cell Lymphoma as Methotrexate-associated Lymphoproliferative Disorders: Case Report

We report a rare case of primary central nervous system (CNS) lymphoma as methotrexate-associated lymphoproliferative disorders (MTX-LPD). A 75-year-old woman who had been treated for rheumatoid arthritis (RA) with MTX for 3 years was admitted to our hospital complaining of unsteady gait, nausea, and vomiting. T2-weighted image of magnetic resonance imaging (MRI) showed multiple high intensity mass-like lesions including right lateral, frontal and temporal lobes, and right cerebellar hemisphere. We performed surgical biopsy, and the pathological and immunohistochemical examinations identified T-cell lymphoma. The tumor regressed and the symptoms were resolved soon after MTX withdrawal. Primary CNS lymphoma due to MTX-LPD is a rare disease and only eight cases including ours are reported.

Characteristics of rheumatoid arthritis with immunodeficiency-associated lymphoproliferative disorders to regress spontaneously by the withdrawal of methotrexate and their clinical course: A retrospective, multicenter, case-control study

OBJECTIVE

To investigate clinical characteristics and time course of lymphoproliferative disorders (LPDs) in rheumatoid arthritis (RA) patients after methotrexate (MTX) discontinuation, in those who achieved spontaneous regression (SR).

METHODS

We retrospectively reviewed clinical data from RA patients with LPDs obtained from eight institutions between 2000 and 2017 and compared clinical and pathological findings between SR and non-SR groups.

RESULTS

Among 232 RA patients with LPDs, 216 were treated with MTX at the onset of LPD and 144 (66.7%) achieved SR after MTX discontinuation. Higher MTX doses, high titers of anti-CCP antibodies (>13.5 U/mL), and lower LDH and soluble IL-2 receptor levels were associated with SR. Lymphocyte count was decreased at LPD onset and increased at 2 weeks after MTX discontinuation in the SR group. Epstein-Barr virus-positive mucocutaneous ulcer, reactive lymphoid hyperplasia and unclassifiable B-cell lymphoma, were more frequent in the SR than in the non-SR group. In multivariable analysis, diffuse large B-cell lymphomas was an independent predictive factor for non-SR. In the patients with SR, 73.9% achieved partial or complete regression as early as 2 weeks after MTX discontinuation.

CONCLUSION

SR and non-SR in RA patients with LPDs after MTX discontinuation were associated with certain clinical characteristics.

Lymphoid and myeloid proliferative disorders associated with inflammatory bowel disease: A clinicopathological study of 15 cases

Lymphoproliferative disorder (LPD) can occur in patients with inflammatory bowel disease (IBD) such as ulcerative colitis (UC) and Crohn's disease (CD). On rare occasion, patients with IBD develop myeloid neoplasms; however, the frequency and clinicopathological features of IBD-associated lymphoid and myeloid proliferative disorder (LMPD) in Japanese patients is still unclear. In this study, we reviewed 2474 Japanese patients with IBD, and found that LMPD occurred in 12 (0.5%) patients with UC (n=7) or CD (n=5). Together with an additional 3 cases, we analyzed a total of 15 cases of LMPD for clinicopathological and histological features. Based on the status of using immunosuppressants such as biologics and immunomodulators, Epstein-Barr virus (EBV) infection, and histopathology, the 15 cases were classified into the Group I (high-grade LPD; n=7), Group II (low-grade LPD; n=5), and Group III (myeloid neoplasms; n=3). Most patients in Group I were undergoing strong immunosuppressive therapy, and the LPD lesions corresponded to high-grade B-cell or T/NK-cell lymphoma often with EBV infection. Discontinuation of immunosuppressive drugs alone did not resolve these LPDs; Group I patients required chemotherapy, and eventually 4 of them (57%) died of the tumor. Most cases in Group II were low-grade B-cell lymphoma without EBV infection and had an indolent clinical course with excellent prognosis. All patients in Group III developed acute myeloid leukemia (AML) during the course of CD. Two (67%) of these patients died of AML. Our study suggests that IBD-associated LMPD is very rare, but can follow an aggressive clinical course.

Safety of long-term use of four common conventional disease modifying anti-rheumatic drugs in rheumatoid arthritis

Conventional disease-modifying antirheumatic drugs (DMARDs) have been used in the management of rheumatoid arthritis for a long time. Whereas methotrexate (MTX) is the anchor drug, leflunomide, hydroxychloroquine and sulfasalazine are used along with MTX either in combination or sequentially. Together these four drugs are the most commonly used DMARDs. They are also used in combination with biological DMARDs (bDMARDs) to enhance their efficacy and MTX in particular to reduce antibodies against anti-tumour necrosis factor. Despite their widespread use, concerns regarding their safety especially when used long-term hinder their optimum use in clinical medicine. In this narrative review we have critically appraised the available literature regarding the safety of these four DMARDs when used long-term.

Rheumatoid arthritis relapse in patients with other iatrogenic immunodeficiency-associated lymphoproliferative disorders and its treatment

OBJECTIVES

Rheumatoid arthritis (RA) in patients undergoing immunosuppressive therapy (IS) is sometimes involved with other iatrogenic immunodeficiency-associated lymphoproliferative disorders (LPD). We aimed to clarify the effects of LPD treatment on RA and the current status of RA treatment options after LPD onset and subsequent IS withdrawal.

METHODS

We retrospectively analyzed data of patients who had RA with LPD and examined the relationship between LPD course and RA treatment as well as that between RA relapse and LPD treatment.

RESULTS

LPD patients were categorized into two groups: patients who regressed spontaneously (n = 19) and those who needed chemotherapy (n = 12). The chemotherapy group had significantly less RA relapse than the spontaneous regression group (p = .041). RA almost relapsed early in the spontaneous regression group and needed treatment for RA. Chemotherapy with rituximab prevented long-term RA relapse, and RA did not relapse for long even after rituximab monotherapy. The total dose of rituximab in monotherapy correlated with the time to RA relapse. Six patients with RA relapse received biologics and had no LPD relapse for more than 1 year.

CONCLUSIONS

Rituximab in chemotherapy for LPD may help prevent RA relapse with LPD. Large-scale studies are required in the future for verification.

Role of Viral Infections in the Pathogenesis of Sjögren's Syndrome: Different Characteristics of Epstein-Barr Virus and HTLV-1

Viruses are possible pathogenic agents in several autoimmune diseases. Sjögren’s syndrome (SS), which involves exocrine dysfunction and the appearance of autoantibodies, shows salivary gland- and lacrimal gland-oriented clinical features. Epstein-Barr virus (EBV) is the most investigated pathogen as a candidate that directly induces the phenotype found in SS. The reactivation of the virus with various stimuli induced a dysregulated form of EBV that has the potential to infect SS-specific B cells and plasma cells that are closely associated with the function of an ectopic lymphoid structure that contains a germinal center (GC) in the salivary glands of individuals with SS. The involvement of human T-cell leukemia virus type 1 (HTLV-1) in SS has been epidemiologically established, but the disease concept of HTLV-1-associated SS remains unexplained due to limited evidence from basic research. Unlike the cell-to-cell contact between lymphocytes, biofilm-like structures are candidates as the mode of HTLV-1 infection of salivary gland epithelial cells (SGECs). HTLV-1 can infect SGECs with enhanced levels of inflammatory cytokines and chemokines that are secreted from SGECs. Regardless of the different targets that viruses have with respect to affinitive lymphocytes, viruses are involved in the formation of pathological alterations with immunological modifications in SS.

Methotrexate-associated lymphoproliferative disorders in the central nervous system and stomach: A case report

RATIONALE

Methotrexate-associated lymphoproliferative disorder (MTX-LPD) is a serious complication in patients treated using methotrexate. It occasionally develops in extra-nodal sites, but rarely in the central nervous system (CNS) or in 2 different sites at the same time. We present the rare case of a patient with rheumatoid arthritis who developed lymphoma in the CNS and stomach during MTX therapy.

PATIENT CONCERNS

A 75-year-old Japanese man with rheumatoid arthritis who received methotrexate was admitted to our hospital because of gait ataxia and anorexia.

DIAGNOSES

Imaging findings and biopsy led to a diagnosis of 2 different types of MTX-LPD in the central nervous system and stomach.

INTERVENTIONS

The lesion in his stomach improved after methotrexate withdrawal, whereas the cerebellar mass required high-dose methotrexate and rituximab therapy.

OUTCOMES

Complete remission has been maintained for the 2 years following the initiation of chemotherapy.

LESSONS

In patients with RA who receive MTX and develop new neurological symptoms, CNS lymphoma as an MTX-LPD may be considered as a differential diagnosis.

Distinct decrease in peripheral lymphocytes in EBER-positive cases of MTX-LPD

OBJECTIVES

To determine the clinical characteristics of methotrexate-associated lymphoproliferative disorder (MTX-LPD).

METHODS

In this study, 12 RA patients who developed MTX-LPD were assessed. The peripheral blood lymphocyte (PBL) count at the onset of MTX-LPD was compared to that 6 months before the onset, in Epstein-Barr virus-encoded RNA (EBER)-positive and -negative subgroups. We examined the change in the PBL count after MTX withdrawal. In patients with relapsed LPD, changes in the PBL count before relapse were also examined.

RESULTS

Regression of LPD after MTX withdrawal was noted in eight patients. In these patients, the PBL count was decreased at the onset of MTX-LPD compared to 6 months before the onset; the decrease was significantly more prominent in EBER-positive patients. In cases of spontaneous regression of LPD, the PBL count recovered quickly after MTX withdrawal. Four of eight patients showed a recurrence of LPD after they improved following MTX withdrawal. These patients also exhibited a decreased PBL count at recurrence compared to 6 months before recurrence.

CONCLUSION

A decrease in the PBL count might be involved in the pathogenesis of MTX-LPD, especially in EBER-positive cases and in patients with LPD relapse after MTX withdrawal following initial improvement.

Rheumatoid Arthritis Complicated with Nasal Septum Perforation Due to Methotrexate-associated Lymphoproliferative Disorder

A 44-year-old female with rheumatoid arthritis treated with methotrexate (MTX) and tocilizumab (TCZ) was admitted to our hospital with nasal pain. Nasal fiberscopy revealed septum perforation, while a membrane biopsy indicated granuloma and fibrinoid necrosis of the small artery. The patient was treated with prednisolone 30 mg/day after discontinuation of MTX and TCZ. Inguinal lymph node biopsy revealed diffuse infiltrations of atypical T-cells and Epstein-Barr virus-positive B cells. The patient was diagnosed with peripheral T-cell lymphoma due to MTX-associated lymphoproliferative disorder (MTX-LPD). We herein describe the case of a patient with nasal septum perforation due to MTX-LPD mimicking granulomatosis with polyangiitis.

[Primary central nervous system methotrexate associated lymphoproliferative disorders in a patient with rheumatoid arthritis]

We report on a 52-year-old woman with rheumatoid arthritis (RA) who developed methotrexate associated lymphoproliferative disorders (MTX-LPD) in the central nervous system (CNS) in the course of immunosuppressive therapy for RA. The patient was admitted because of monoplegia in her left hand. She had been receiving methotrexate (MTX) for her RA for several years and etanercept had also been introduced because of a worsening of the arthritis six months before admission. Brain MRI revealed multiple lesions with enhancement scattered throughout both hemispheres. ¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography showed abnormal accumulation suggesting malignancy in the right frontal lobe where abnormal enhancement was observed on the MRI. A brain biopsy was performed at the identified site and it confirmed diffuse large B-cell lymphoma (DLBCL). We therefore diagnosed her as MTX-LPD. According to previous reports, most MTX-LPD cases tend to show regression after the cessation of MTX. However, our case showed no regression and even needed chemotherapy. The patient had a poorer prognosis than previous cases and died 17 months after the onset. Although it is an uncommon complication, particularly in the CNS, MTX-LPD should be considered as a critical differential diagnosis if a patient receiving MTX develops central nervous system lesions. Immediate medical intervention including brain biopsy is required.

Lymphoproliferative disorder in an elderly rheumatoid arthritis patient after longterm oral methotrexate administration: A case report

Methotrexate-associated lymphoproliferative disorder (MTX-LPD) is frequently reported in the literature; however, its pathophysiology has not been fully elucidated to date. We herein describe a case of MTX-LPD that occurred after long-term treatment with oral MTX in a 67-year-old Japanese woman with rheumatoid arthritis (RA) who presented with generalized lymphadenopathy of the neck. The patient had been diagnosed with RA 24 years earlier, and had been on oral MTX for 20 years. The patient noticed a mass on her neck, which prompted a visit to our hospital. The mass was confirmed as diffuse large B-cell lymphoma by biopsy. MTX treatment was discontinued, which resulted in a reduction in the size of the mass and improvement of the patient's symptoms. Therefore, clinicians must be aware of MTX-LPD as a differential diagnosis for patients with rheumatological conditions on long-term MTX therapy presenting with signs and symptoms suggestive of lymphoma.

Lymphoproliferative disorders in patients with rheumatoid arthritis in the era of widespread use of methotrexate: A review of the literature and current perspective

Lymphoproliferative disorders (LPD) in patients receiving methotrexate (MTX) have gained strong attention. In this article, I reviewed the basic and clinical findings of this issue. Patients with RA possess a high risk of lymphoma, but epidemiological evidence showing an association between the use of MTX and lymphoma is still limited. Rapid regression of LPD after stopping MTX in patients with RA strongly suggests that there is a causative relationship. Genetic predisposition, accumulated inflammation, impaired generation of Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes, effects of MTX on the regulation of EBV genes, and low hypermethylation of apoptosis-related genes are relevant to the development of LPD and rapid regression after cessation of MTX. The clinical and histological characteristics of LPD in RA patients who are treated with MTX have been established, and recent data indicate that initial cessation of MTX and watchful waiting to observe an increase in peripheral lymphocyte counts have a therapeutic value. In advanced cases, various chemotherapy regimens are used, and consultation with hematologists is recommended to select the optimal treatment. There is no consensus on the treatment of RA after development of LPD, and long-term observation is necessary to investigate the safety of disease-modifying antirheumatic drugs in these patients.