Urticarial mycosis fungoides: A distinctive presentation with blood involvement and a peculiar immunophenotype.

Mycosis fungoides (MF) has been widely reported to mimick a considerable number of different dermatoses, including scarring alopecia, bullous dermatoses or cysts, and comedones. In atypical presentations, histopathology is essential for the diagnosis. We present two cases of MF with clinical urticarial lesions and a striking blood involvement that responded to mogamulizumab treatment. Histopathologically, both cases had classic MF features and shared a peculiar immunophenotype, with positivity for CD25 and FOXP3. Differential diagnoses included urticarial lymphomatoid drug reactions and other lymphomas, like T-cell prolymphocytic leukemia, atypical Sézary syndrome, or adult T-cell lymphocytic leukemia. A low suspicion threshold is necessary for the diagnosis of atypical presentations of MF.

Mogamulizumab-associated rash - Case series and review of the literature.

Mogamulizumab, a monoclonal antibody directed against CC chemokine receptor 4, is approved as a second-line treatment of mycosis fungoides and Sézary syndrome. One of the most common side effects is mogamulizumab-associated rash (MAR), which can present in a variety of clinical and histological types. Clinically, it can be difficult to differentiate between MAR and progression of the underlying disease, so histological examination is crucial for clinicopathological correlation. Current data analyses suggest that MAR is more common in patients with Sézary syndrome and is associated with a significantly better response to treatment, making the distinction from disease progression particularly important. The management of MAR depends on its severity, and therapy may need to be paused. This article presents three cases from our clinic and reviews the current literature on MAR. It emphasizes the importance of understanding MAR in the management of patients with cutaneous lymphomas.

Cost of Treating Cutaneous T-Cell Lymphoma in Spain: Analysis of MICADOS Study Data by Disease Stage. / Evaluación de los costes asociados a la enfermedad de pacientes con linfoma cutáneo de células T en España: análisis en función del estadio clínico (estudio MICADOS).

BACKGROUND AND OBJECTIVE: The cost of treating cutaneous T-cell lymphoma (CTCL) in Spain is unknown. With the advent of new treatments, it is more important than ever to gain an accurate picture of the true costs involved. The MICADOS study had 2 primary objectives: 1)to evaluate the impact of CTCL on patient quality of life, and 2)to evaluate the costs associated with the disease. This article reports the results of the cost analysis. METHODS: We estimated the cost of treating CTCL over a period of 1year from the perspective of the Spanish National Health System. Twenty-three dermatologists and hematologists from 15 public hospitals analyzed data for adult patients with mycosis fungoides (MF) or Sézary syndrome (SS). RESULTS: A total of 141 patients (57.4% male) with a mean age of 63.6 years (95%CI: 61.4-65.7 years) were included. The mean direct annual cost of treating CTCL was €34,214 per patient. The corresponding costs by stage were €11,952.47 for stageI disease, €23,506.21 for stageII disease, €38,771.81 for stageIII disease, and €72,748.84 for stageIV disease. The total direct annual cost of treating MF/SS in public hospitals in Spain was estimated at €78,301,171; stageI disease accounted for 81% of all costs, stageII for 7%, and stagesIII andIV for 6% each. CONCLUSIONS: The MICADOS study offers an accurate picture of the direct cost of treating CTCL in patients with MF/SS in Spain and shows that costs vary significantly according to disease stage. Patient-borne and indirect costs should be analyzed in future studies.

[Translated article] Cost of Treating Cutaneous T-Cell Lymphoma in Spain: Analysis of MICADOS Study Data by Disease Stage.

BACKGROUND AND OBJECTIVE: The cost of treating cutaneous T-cell lymphoma (CTCL) in Spain is unknown. With the advent of new treatments, it is more important than ever to gain an accurate picture of the true costs involved. The MICADOS study had 2 primary objectives: 1)to evaluate the impact of CTCL on patient quality of life, and 2)to evaluate the costs associated with the disease. This article reports the results of the cost analysis. METHODS: We estimated the cost of treating CTCL over a period of 1year from the perspective of the Spanish National Health System. Twenty-three dermatologists and hematologists from 15 public hospitals analyzed data for adult patients with mycosis fungoides (MF) or Sézary syndrome (SS). RESULTS: A total of 141 patients (57.4% male) with a mean age of 63.6 years (95%CI: 61.4-65.7 years) were included. The mean direct annual cost of treating CTCL was €34,214 per patient. The corresponding costs by stage were €11,952.47 for stageI disease, €23,506.21 for stageII disease, €38,771.81 for stageIII disease, and €72,748.84 for stageIV disease. The total direct annual cost of treating MF/SS in public hospitals in Spain was estimated at €78,301,171; stageI disease accounted for 81% of all costs, stageII for 7%, and stagesIII andIV for 6% each. CONCLUSIONS: The MICADOS study offers an accurate picture of the direct cost of treating CTCL in patients with MF/SS in Spain and shows that costs vary significantly according to disease stage. Patient-borne and indirect costs should be analyzed in future studies.

[[Translated article]]Survival Analysis and Prognostic Factors in a Case Series of 148 Cutaneous T-Cell Lymphomas. / Análisis de supervivencia y factores pronósticos en una serie de 148 casos de linfomas cutáneos de células T.

BACKGROUND AND OBJECTIVE: Cutaneous T-cell lymphomas (CTCL) such as mycosis fungoides (MF) and Sézary syndrome (SS) are rare lymphomas with varying prognoses. The aim of the study was to describe the survival of a cohort of patients with MF/SS and evaluate the prognostic factors impacting disease survival. MATERIALS AND METHODS: All cases of MF/SS diagnosed from 2008 through 2022 were retrospectively analyzed. The demographic variables, histological parameters, and analytical data were analyzed too. Progression-free survival (PFS) and disease-specific survival (DSS) were calculated. RESULTS: A total of 148 cases were included. A total of 121 (82%) and 27 cases were diagnosed with MF, and SS, respectively. A total of 37 patients (25%) experienced progression at some point disease progression. The median PFS and median DSS were 127 and 135 months, respectively. Age > 60 years, diagnosis of SS, the presence of large cell transformation (LCT) at diagnosis, folliculotropism in early stages, high Ki-67 expression, the presence of the clonal T-cell receptor (TCR) in blood, elevated LDH and B2M levels, and advanced stages (IIB, IVA, T3, T4, N3/Nx) were associated with worse prognosis across the entire cohort. CONCLUSIONS: Stage IVA and the presence of LCT at diagnosis stood out as independent factors of unfavorable prognosis. LCT was the variable that most significantly impacted the patients' survival and was closely associated with tumor skin involvement and stage IIB.

Experience With Bexarotene to Treat Cutaneous T-Cell Lymphomas: A Study of the Spanish Working Group of Cutaneous Lymphomas.

BACKGROUND AND OBJECTIVES: Bexarotene has been approved to treat advanced stage cutaneous T-cell lymphomas (CTCL) since 1999. However, very few data have been published on its long-term safety and efficacy profile. The aim of this study is to determine the tolerability to bexarotene and outcomes by collecting the 2nd largest case series to date on its long-term use vs CTCL. MATERIAL AND METHOD: This was a multicenter retrospective review of 216 patients with mycosis fungoides (174), or Sézary syndrome (42) on a 10-year course of bexarotene alone or in combination with other therapies at 19 tertiary referral teaching hospitals. RESULTS: A total of 133 men (62%) and 83 women (38%) were included, with a mean age of 63.5 year (27-95). A total of 45% were on bexarotene monotherapy for the entire study period, 22% started on bexarotene but eventually received an additional therapy, 13% were on another treatment but eventually received bexarotene while the remaining 20% received a combination therapy since the beginning. The median course of treatment was 20.78 months (1-114); and the overall response rate, 70.3%. Complete and partial response rates were achieved in 26% and 45% of the patients, respectively. Treatment was well tolerated, being the most common toxicities hypertriglyceridemia (79%), hypercholesterolemia (71%), and hypothyroidism (52%). No treatment-related grade 5 adverse events were reported. CONCLUSIONS: Our study confirms bexarotene is a safe and effective therapy for the long-term treatment of CTCL.

Experience With Bexarotene to Treat Cutaneous T-Cell Lymphomas: A Study of the Spanish Working Group of Cutaneous Lymphomas. / [Artículo traducido] Experiencia con bexaroteno en linfoma cutáneo de células T: un estudio del Grupo Español de Linfomas Cutáneos (GELC).

BACKGROUND AND OBJECTIVES: Bexarotene has been approved to treat advanced stage cutaneous T-cell lymphomas (CTCL) since 1999. However, very few data have been published on its long-term safety and efficacy profile. The aim of this study is to determine the tolerability to bexarotene and outcomes by collecting the 2nd largest case series to date on its long-term use vs CTCL. MATERIAL AND METHOD: This was a multicenter retrospective review of 216 patients with mycosis fungoides (174), or Sézary syndrome (42) on a 10-year course of bexarotene alone or in combination with other therapies at 19 tertiary referral teaching hospitals. RESULTS: A total of 133 men (62%) and 83 women (38%) were included, with a mean age of 63.5 year (27-95). A total of 45% were on bexarotene monotherapy for the entire study period, 22% started on bexarotene but eventually received an additional therapy, 13% were on another treatment but eventually received bexarotene while the remaining 20% received a combination therapy since the beginning. The median course of treatment was 20.78 months (1-114); and the overall response rate, 70.3%. Complete and partial response rates were achieved in 26% and 45% of the patients, respectively. Treatment was well tolerated, being the most common toxicities hypertriglyceridemia (79%), hypercholesterolemia (71%), and hypothyroidism (52%). No treatment-related grade 5 adverse events were reported. CONCLUSIONS: Our study confirms bexarotene is a safe and effective therapy for the long-term treatment of CTCL.

Molecular pathogenesis of Cutaneous T cell Lymphoma: Role of chemokines, cytokines, and dysregulated signaling pathways.

Cutaneous T cell lymphomas (CTCLs) are a heterogeneous group of lymphoproliferative neoplasms that exhibit a wide spectrum of immune-phenotypical, clinical, and histopathological features. The biology of CTCL is complex and remains elusive. In recent years, the application of next-generation sequencing (NGS) has evolved our understanding of the pathogenetic mechanisms, including genetic aberrations and epigenetic abnormalities that shape the mutational landscape of CTCL and represent one of the important pro-tumorigenic principles in CTCL initiation and progression. Still, identification of the major pathophysiological pathways including genetic and epigenetic components that mediate malignant clonal T cell expansion has not been achieved. This is of prime importance given the role of malignant T cell clones in fostering T helper 2 (Th2)-bias tumor microenvironment and fueling progressive immune dysregulation and tumor cell growth in CTCL patients, manifested by the secretion of Th2-associated cytokines and chemokines. Alterations in malignant cytokine and chemokine expression patterns orchestrate the inflammatory milieu and influence the migration dynamics of malignant clonal T cells. Here, we highlight recent insights about the molecular mechanisms of CTCL pathogenesis, emphasizing the role of cytokines, chemokines, and associated downstream signaling networks in driving immune defects, malignant transformation, and disease progression. In-depth characterization of the CTCL immunophenotype and tumoral microenvironment offers a facile opportunity to expand the therapeutic armamentarium of CTCL, an intractable malignant skin disease with poor prognosis and in dire need of curative treatment approaches.

Staging lymph nodes and blood at diagnosis in mycosis fungoides identifies patients at increased risk of progression to advanced stage: A retrospective cohort study.

BACKGROUND: Risk factors for progression to advanced-stage mycosis fungoides (MF) are poorly defined. METHODS: The authors performed a single-center, retrospective cohort study among patients with MF at an academic medical center from 1990 to 2020 to identify clinical variables associated with progression to advanced-stage MF (stage IIB-IVB), and 388 patients who had a clinicopathologic diagnosis of early stage (IA-IIA) MF were identified from their cutaneous lymphoma database. Baseline clinical characteristics, laboratory values, imaging, and blood flow cytometry or T-cell receptor gene rearrangement (TCR) data were collected. Logistic regression was used to assess risk factors associated with progression. RESULTS: Overall, 93 of 388 patients (24.0%) progressed to advanced stage. Patients who progressed had an increased risk of death (hazard ratio, 4.50; 95% CI, 2.89-7.00; p < .001). Progression was associated with a higher overall stage at diagnosis, tumor stage, lymph node stage, low-level blood involvement, as measured with TCR data and/or flow cytometry, and elevated lactate dehydrogenase (LDH). Limitations included missing data for LDH, imaging, peripheral blood TCR data, or flow cytometry assessed at diagnosis. CONCLUSIONS: Staging and baseline laboratory assessments with imaging, peripheral blood flow cytometry, TCR data, and LDH in patients who have newly diagnosed MF may identify those who are at risk for progression to advanced stage.

Mogamulizumab-Associated Myositis With and Without Myasthenia Gravis and/or Myocarditis in Patients With T-Cell Lymphoma.

Mogamulizumab is being increasingly prescribed for the treatment of T-cell lymphomas (MF/SS/ATLL). We conducted a retrospective cohort study to identify muscular immune-related adverse events (irAEs) associated with mogamulizumab in patients with T-cell lymphoma followed at Dana-Farber Cancer Institute from January 2015 to June 2022. We identified 5 cases of mogamulizumab-associated myositis and/or myocarditis (MAM/Mc), 2 additionally affected by myasthenia gravis, among 42 patients with T-cell lymphoma. Three cases experienced -mogamulizumab-associated rash (MAR) prior to developing MAM/Mc. The incidence (n = 5/42, 11.9%) of muscular mogamulizumab-associated irAEs may be higher than has been previously reported in clinical trials and may be of late onset (a median of 5 cycles and as late as 100 days from the last infusion). We highlight the utility of IVIG, together with systemic corticosteroids, for the treatment of these potentially fatal side effects associated with mogamulizumab therapy.

Complete Response to tenalisib and romidepsin with long-term maintenance using tenalisib monotherapy in a patient with relapsed and refractory sézary syndrome.

Mycosis fungoides (MF) and Sézary Syndrome (SS) are the most common subtypes of cutaneous T cell lymphomas (CTCL). Advanced-stage MF/SS have poor prognoses and may be refractory to multiple systemic treatments. These cases can be difficult to achieve and maintain complete response and there is a need for novel therapeutics. Inhibition of the phosphatidylinositol 3-kinase (PI3K) pathway by Tenalisib presents one such emerging drug. We report a relapsed/refractory SS patient achieving complete remission using the combination of Tenalisib and Romidepsin and subsequently maintaining long-duration CR with Tenalisib monotherapy.

Early intervention of extracorporeal photopheresis for advancing/progressing cutaneous T-cell lymphoma.

Patients with cutaneous T-cell lymphoma with progressive disease typically undergo a series of skin-directed and systemic therapy regimens during cycles of response and relapse. Extracorporeal photopheresis (ECP) is an effective and safe systemic treatment option, often reserved for later stages of disease and typically employed after failure of several other therapies. ECP has benefits in response rate, time to next treatment, and tolerability that may support its use earlier in the treatment cycle for advancing/progressing disease.

Clinical Outcomes of COVID-19 in Mycosis Fungoides and Sezary Syndrome.

INTRODUCTION: Haemato-oncologic patients are more susceptible to severe infections with SARS-CoV-2. We aimed to assess the clinical outcomes of SARS-CoV-2 infection among patients with Mycosis Fungoides and Sezary Syndrome (MF/SS). METHODS: The data were retrieved from anonymized electronic medical records of Maccabi Healthcare Services (MHS), the second-largest healthcare organization in Israel. Patients diagnosed with MF/SS were included in the study. COVID-19 PCR test results together with sociodemographic and clinical data were extracted and analyzed to evaluate the association of COVID-19 with clinical outcomes. RESULTS: In the period of 2020-2022, 1,472 MF/SS patients were included in the study. Among them, 768 (52%) had SARS-CoV-2 infection. The hospitalization rate was 2.9% and infection by the Delta variant was associated with the highest hospitalization rate (7.7%). The hospitalization rate was lower among fully vaccinated patients (p = 0.032) but higher for patients older than 65 (p < 0.001) and patients with SS (vs. MF) (p < 0.001) or COPD (p = 0.024) diagnosis. There was a tendency for decreased hospitalization among patients treated with nirmatrelvir + ritonavir within 5 days of infection, with a 79% risk reduction, although it was not statistically significant (p = 0.164). CONCLUSION: Patients with MF/SS do not necessarily have worse COVID-19 outcomes compared to the general population.

High-throughput RNA sequencing of the T cell receptor alpha and beta chains for simultaneous clonality and biological analyses in Sezary syndrome.

BACKGROUND: Previous investigations pointed out a role for antigen stimulation in Sezary syndrome (SS). High-throughput sequencing of the T cell receptor (TR) offers several applications beyond diagnostic purposes, including the study of T cell pathogenesis. METHODS: We performed high-throughput RNA sequencing of the TR alpha (TRA) and beta (TRB) genes focusing on the complementarity-determining region 3 (CDR3) in 11 SS and one erythrodermic mycosis fungoides (MF) patients. Five psoriasis patients were employed as controls. Peripheral blood CD4+ cells were isolated and RNA sequenced (HiSeq2500). High-resolution HLA typing was performed in neoplastic patients. RESULTS: Highly expanded predominant TRA and TRB CDR3 were only found in SS patients (median frequency: 94.4% and 93.7%). No remarkable CDR3 expansions were observed in psoriasis patients (median frequency of predominant TRA and TRB CDR3: 0.87% and 0.69%, p < 0.001 compared to SS). CDR3 almost identical to the predominant were identified within each SS patient and were exponentially correlated with frequencies of the predominant CDR3 (R2 = 0.918, p < 0.001). Forty-six different CDR3 were shared between SS patients displaying HLA similarities, including predominant TRA and TRB CDR3 in one patient that were found in other three patients. Additionally, 351 antigen matches were detected (Cytomegalovirus, Epstein-Barr, Influenza virus, and self-antigens), and the predominant CDR3 of two different SS patients matched CDR3 with specificity for Influenza and Epstein-Barr viruses. CONCLUSIONS: Besides detecting clonality, these findings shed light on the nature of SS-related antigens, pointing to RNA sequencing as a useful tool for simultaneous clonality and biological analysis in SS.

TMEM244 Is a Long Non-Coding RNA Necessary for CTCL Cell Growth.

Transmembrane protein 244 (TMEM244) was annotated to be a member of the TMEM family, which are is a component of cell membranes and is involved in many cellular processes. To date, the expression of the TMEM244 protein has not been experimentally confirmed, and its function has not been clarified. Recently, the expression of the TMEM244 gene was acknowledged to be a diagnostic marker for Sézary syndrome, a rare cutaneous T-cell lymphoma (CTCL). In this study, we aimed to determine the role of the TMEM244 gene in CTCL cells. Two CTCL cell lines were transfected with shRNAs targeting the TMEM244 transcript. The phenotypic effect of TMEM244 knockdown was validated using green fluorescent protein (GFP) growth competition assays and AnnexinV/7AAD staining. Western blot analysis was performed to identify the TMEM244 protein. Our results indicate that TMEM244 is not a protein-coding gene but a long non-coding RNA (lncRNA) that is necessary for the growth of CTCL cells.

Imbalanced IL-1B and IL-18 Expression in Sézary Syndrome.

Sézary syndrome (SS) is a rare and aggressive type of cutaneous T-cell lymphoma, with an abnormal inflammatory response in affected skin. The cytokines IL-1B and IL-18, as key signaling molecules in the immune system, are produced in an inactive form and cleave to the active form by inflammasomes. In this study, we assessed the skin, serum, peripheral mononuclear blood cell (PBMC) and lymph-node samples of SS patients and control groups (healthy donors (HDs) and idiopathic erythroderma (IE) nodes) to investigate the inflammatory markers IL-1B and IL-18 at the protein and transcript expression levels, as potential markers of inflammasome activation. Our findings showed increased IL-1B and decreased IL-18 protein expression in the epidermis of SS patients; however, in the dermis layer, we detected increased IL-18 protein expression. In the lymph nodes of SS patients at advanced stages of the disease (N2/N3), we also detected an enhancement of IL-18 and a downregulation of IL-1B at the protein level. Moreover, the transcriptomic analysis of the SS and IE nodes confirmed the decreased expression of IL1B and NLRP3, whereas the pathway analysis indicated a further downregulation of IL1B-associated genes. Overall, the present findings showed compartmentalized expressions of IL-1B and IL-18 and provided the first evidence of their imbalance in patients with Sézary syndrome.

The effect of mogamulizumab on the aberrant T cell population in the peripheral blood - A monocentric retrospective analysis.

BACKGROUND AND OBJECTIVES: The effect of mogamulizumab in cutaneous T-cell lymphoma (CTCL) on T cells (TC) in the peripheral blood and its potential role to navigate treatment intervals are explored. METHODS: We investigated within a retrospective monocentric analysis the effect of mogamulizumab on the CD3+ TC and the aberrant T cell population (TCP), i.e., the CD4+ /CD7- and the CD4+ /CD26- TC, analyzed by flow cytometry. RESULTS: Thirteen patients with CTCL were included. After four cycles there was a mean reduction of 57% in CD3+ TC, 72% in the CD4+ /CD7- and 75% in the CD4+ /CD26- TCP compared to the individual baseline of each patient. The reduction in CD4+ /CD7+ and CD4+ /CD26+ TC was lower, averaging 54% and 41%. A significant decrease in aberrant TCP was already evident after the first administration. A median plateau of TCP already occurred during the IP. Progressive disease occurred in 5/13 patients without a clear correlation to aberrant TCP. CONCLUSIONS: Already after one dose of mogamulizumab, aberrant TCP and, to a lesser extent, normal TC decrease. We did not observe a clear correlation between TCP and the efficacy of mogamulizumab, but further studies with larger numbers of patients are needed.

Epidemiology of mature T/NK-cell lymphomas in Germany - A representative cross-sectional study based on SHI claims data.

BACKGROUND: Primary cutaneous lymphomas (PCL) are rare skin tumors of lymphoproliferative neoplasms and belong to the heterogeneous group of non-Hodgkin's lymphomas. PCL encompass a broad spectrum of clinical and histologic manifestations, with cutaneous T-cell lymphoma (CTCL) being the most common (73%). Due to the rarity of the diseases, population-based studies of care and epidemiology are limited. PATIENTS AND METHODS: Based on anonymized, age- and sex-adjusted SHI (statutory health insurance) claims data of approximately five million SHI-insured patients, a retrospective analysis was conducted over a six-year period (2012-2017) to determine the prevalence, incidence, and lethality in patients with mature-cell T/NK-cell lymphoma in Germany. RESULTS: A total of 1,336 patients with T-cell lymphoma were identified during the observation period. The six-year prevalence ranged from 27.35 to 43.58 per 100,000. Patients were 65% male with a mean age of 66 years (SD 15). There were 246 patients (approx. 20%) who died within the 6 years, up to 7% per year. The calculated incidence in 153 identified patients in 2017 is 3.65 to 3.92 per 100,000. CONCLUSIONS: For the first time, valid epidemiologic findings of patients with mature T-cell and NK-cell lymphomas were obtained using SHI claims data in Germany. Further analyses are needed to gain a deeper insight into the healthcare reality of patients with this rare disease.

Survival Analysis and Prognostic Factors in a Case Series of 148 Cutaneous T-Cell Lymphomas. / Análisis de supervivencia y factores pronósticos en una serie de 148 casos de linfomas cutáneos de células T.

BACKGROUND AND OBJECTIVE: Cutaneous T-cell lymphomas (CTCL) such as mycosis fungoides (MF) and Sézary syndrome (SS) are rare lymphomas with varying prognoses. The aim of the study was to describe the survival of a cohort of patients with MF/SS and evaluate the prognostic factors impacting disease survival. MATERIALS AND METHODS: All cases of MF/SS diagnosed from 2008 through 2022 were retrospectively analyzed. The demographic variables, histological parameters, and analytical data were analyzed too. Progression-free survival (PFS) and disease-specific survival (DSS) were calculated. RESULTS: A total of 148 cases were included. A total of 121 (82%) and 27 cases were diagnosed with MF, and SS, respectively. A total of 37 patients (25%) experienced progression at some point disease progression. The median PFS and median DSS were 127 and 135 months, respectively. Age >60 years, diagnosis of SS, the presence of large cell transformation (LCT) at diagnosis, folliculotropism in early stages, high Ki-67 expression, the presence of the clonal T-cell receptor (TCR) in blood, elevated LDH and B2M levels, and advanced stages (IIB, IVA, T3, T4, N3/Nx) were associated with worse prognosis across the entire cohort. CONCLUSIONS: Stage IVA and the presence of LCT at diagnosis stood out as independent factors of unfavorable prognosis. LCT was the variable that most significantly impacted the patients' survival and was closely associated with tumor skin involvement and stage IIB.

CCR4 in cutaneous T-cell lymphoma: Therapeutic targeting of a pathogenic driver.

New treatments are needed for patients with cutaneous T-cell lymphoma (CTCL), particularly for advanced mycosis fungoides (MF) and Sezary syndrome (SS). The immunopathology of MF and SS is complex, but recent advances in tumor microenvironment understanding have identified CCR4 as a promising therapeutic target. CCR4 is widely expressed on malignant T cells and Tregs in the skin and peripheral blood of patients with MF and SS. The interaction of CCR4 with its dominant ligands CCL17 and CCL22 plays a critical role in the development and progression of CTCL, facilitating the movement into, and accumulation of, CCR4-expressing T cells in the skin, and recruiting CCR4-expressing Tregs into the tumor microenvironment. Expression of CCR4 is upregulated at all stages of MF and in SS, increasing with advancing disease. Several CCR4-targeted therapies are being evaluated, including "chemotoxins" targeting CCR4 via CCL17, CCR4-directed chimeric antigen receptor-modified T-cell therapies, small-molecule CCR4 antagonists, and anti-CCR4 monoclonal antibodies. Only one is currently approved: mogamulizumab, a defucosylated, fully humanized, anti-CCR4, monoclonal antibody for the treatment of relapsed/refractory MF and SS. Clinical trial da1ta confirm that mogamulizumab is an effective and well-tolerated treatment for relapsed/refractory MF or SS, demonstrating the clinical value of targeting CCR4.