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Patients with advanced-stage mycosis fungoides (MF IIB–IVB) and Sézary syndrome (SS) have poor prognoses, with survival ranging from 4.7 to 1.4 years depending on the disease stage. There is a need for therapeutic approaches that lead to long-lasting responses and improved quality of life and survival. Mogamulizumab, a humanized antibody against the CCR4 molecule, and low-dose total skin electron beam therapy (TSEBT) are two known established treatments for MF and SS as a monotherapy. However, little is known about the potential additive effect on the combination of both treatments. We report here for the first time the concurrent use of low-dose hypofractionated TSEBT (2 × 4 Gy) with mogamulizumab. Based on two relapsed/refractory and advanced-stage CTCL patients, we show that this combination may be well tolerated in advanced-stage MF or SS and may potentially lead to an additive treatment effect on response times, particularly in the skin and blood within two weeks. We propose that this combination may be a treatment option for patients with SS. Further research is needed to understand the efficacy and tolerability profile of this therapeutic combination and to determine if there is an additive effect of the combination on the response rates when compared with the monotherapy. [ABSTRACT FROM AUTHOR]

Mogamulizumab is an anti-C–C chemokine receptor 4 antibody that is increasingly being used to treat T-cell malignancies such as cutaneous T-cell lymphoma, adult T-cell leukemia-lymphoma, and peripheral T-cell lymphoma. Because CCR4 is expressed on both malignant T-cells and regulatory T-cells (Tregs), mogamulizumab can be associated with increased immune-related adverse events (irAEs). While there is abundant literature on mogamulizumab-associated rash (MAR) and graft-versus-host disease (GVHD), other reported irAEs have not been collated into a single review. This narrative review covers irAEs associated with mogamulizumab in patients with T-cell lymphomas, focusing on events other than MAR and GVHD. We searched PubMed and Google Scholar for case reports, case series, chart reviews, and clinical trials published from inception to March 2024. Identified events include alopecia, vitiligo, arthritis, psoriasis, myocarditis, myositis/polymyositis, hepatitis, and others. Mogamulizumab's ability to augment the host immune response through Treg depletion adds to its efficacy but has wide-ranging implications for autoimmunity across multiple organ systems, similar to immune checkpoint inhibitor therapy. Occurrence of irAEs may be associated with improved overall clinical response, although long-term follow-up studies are needed. [ABSTRACT FROM AUTHOR]

Abstract Introduction Sézary syndrome (SS) is a rare leukemic cutaneous T cell lymphoma. This study was conducted to examine the real-world treatment patterns among patients with SS in the USA from 2018 to 2020. Methods This was a retrospective cohort study using the Symphony Health Solutions claims database. Adult patients with ≥ 1 diagnosis code for SS were classified into three non-mutually exclusive cohorts: 2018, 2019, and 2020. Patient characteristics and treatment patterns were examined across the 3 years of study and reported descriptively for each year. Annual treatment patterns were also described for the five states with the highest proportions of SS patients in 2020. Results Overall, 869, 882, and 853 SS patients were identified in 2018, 2019, and 2020, respectively (median age: 70 years for each year; male: 54.4%, 54.8%, and 55.6%, respectively). The use of any systemic and parenteral systemic treatments increased over time. While utilization rates for many specific systemic therapies decreased over the study period, mogamulizumab use increased, making it the most commonly used systemic treatment in 2020 (29.2%) among patients with any systemic treatment. The five states with the highest proportions of SS patients in 2020 were Florida, New York, California, Texas, and Pennsylvania. Systemic treatment patterns varied considerably by state. Conclusion Some systemic therapies showed decreased usage over time while a few showed increased utilization, with mogamulizumab showing the largest increase. Treatment patterns for SS varied by region. Further research is needed to examine the factors that drive treatment selection for patients with SS.

Patients with advanced-stage mycosis fungoides (MF IIB–IVB) and Sézary syndrome (SS) have poor prognoses, with survival ranging from 4.7 to 1.4 years depending on the disease stage. There is a need for therapeutic approaches that lead to long-lasting responses and improved quality of life and survival. Mogamulizumab, a humanized antibody against the CCR4 molecule, and low-dose total skin electron beam therapy (TSEBT) are two known established treatments for MF and SS as a monotherapy. However, little is known about the potential additive effect on the combination of both treatments. We report here for the first time the concurrent use of low-dose hypofractionated TSEBT (2 × 4 Gy) with mogamulizumab. Based on two relapsed/refractory and advanced-stage CTCL patients, we show that this combination may be well tolerated in advanced-stage MF or SS and may potentially lead to an additive treatment effect on response times, particularly in the skin and blood within two weeks. We propose that this combination may be a treatment option for patients with SS. Further research is needed to understand the efficacy and tolerability profile of this therapeutic combination and to determine if there is an additive effect of the combination on the response rates when compared with the monotherapy.

Due to the poor prognosis of adult T-cell leukemia/lymphoma (ATL), new treatments are urgently needed, especially for elderly patients with aggressive ATL. The anti-CCR4 antibody drug mogamulizumab (MOG) has been approved for the treatment of untreated ATL. To analyze the impact of MOG on elderly patients, we conducted a retrospective analysis of patients aged 70 years and older with aggressive ATL diagnosed at our institution between 2015 and 2021. Among 32 patients, including those who received best supportive care, the median survival time (MST) and 2-year overall survival (OS) rate were 14.6 months (range, 0.0–83.7), and 34.7% [95% confidence interval (CI), 18.2–51.9], respectively, which were better than outcomes in our previous study. The MST and 2-year OS for patients treated with MOG-containing chemotherapy were 18.1 months (range, 4.0–83.7) and 45.0% (95%CI, 23.1–64.7), respectively, demonstrating clear improvement. Adverse events observed with MOG-containing treatment, such as myelosuppression and skin rash, were similar to those reported previously. Univariate analysis identified comorbidity as a predictor of poor outcomes, but not intensity of MOG-containing treatment, suggesting a different mechanism of action than that of classical chemotherapy. Our study suggests that MOG-containing treatments are an option for elderly patients with ATL. [ABSTRACT FROM AUTHOR]

Introduction: Sézary syndrome (SS) is a rare leukemic cutaneous T cell lymphoma. This study was conducted to examine the real-world treatment patterns among patients with SS in the USA from 2018 to 2020. Methods: This was a retrospective cohort study using the Symphony Health Solutions claims database. Adult patients with ≥ 1 diagnosis code for SS were classified into three non-mutually exclusive cohorts: 2018, 2019, and 2020. Patient characteristics and treatment patterns were examined across the 3 years of study and reported descriptively for each year. Annual treatment patterns were also described for the five states with the highest proportions of SS patients in 2020. Results: Overall, 869, 882, and 853 SS patients were identified in 2018, 2019, and 2020, respectively (median age: 70 years for each year; male: 54.4%, 54.8%, and 55.6%, respectively). The use of any systemic and parenteral systemic treatments increased over time. While utilization rates for many specific systemic therapies decreased over the study period, mogamulizumab use increased, making it the most commonly used systemic treatment in 2020 (29.2%) among patients with any systemic treatment. The five states with the highest proportions of SS patients in 2020 were Florida, New York, California, Texas, and Pennsylvania. Systemic treatment patterns varied considerably by state. Conclusion: Some systemic therapies showed decreased usage over time while a few showed increased utilization, with mogamulizumab showing the largest increase. Treatment patterns for SS varied by region. Further research is needed to examine the factors that drive treatment selection for patients with SS. [ABSTRACT FROM AUTHOR]

Treatment with CCR-4 antagonists has been shown to be protective against the development of invasive pulmonary aspergillosis in animal models. Herein, we present a case of fatal invasive pulmonary aspergillosis in a patient receiving Mogamulizumab. A 64-year-old man with refractory mycosis fungoides was found to have diffuse bilateral pulmonary nodules during a chest CT in June 2022. Bronchoalveolar lavage (BAL) fungal and bacterial cultures and galactomannan were negative, as well as serum beta-glucan and galactomannan. Histology showed a lymphoid infiltrate with a negative fungal stain, so a presumptive diagnosis of lymphoma infiltration was made, and the patient started the CCR-4 antagonist Mogamulizumab treatment in August 2022. He had no symptoms until November when he presented to the hematology clinic reporting dyspnea. He had neutrophilic leukocytosis (18.610 cells/µL), his c-reactive protein was 27 mg/dL, and his skin lesions from mycosis fungoides were just starting to improve. A CT scan showed large diffuse bilateral severely necrotic cavitated lesions with thick walls and apparently synchronous evolution. Beta-glucan was 31 pg/mL (wako method), while serum galactomannan 3.6. BAL was positive for Aspergillus fumigatus culture and galactomannan. Patient started voriconazole but, despite being in a stable condition, he suddenly died after two days. Discussion: Paradoxically, worsening of the chronic pulmonary aspergillosis has been reported after nivolumab treatment, and immune reconstitution syndromes are usually seen during neutrophil recovery after intensive chemotherapy. Our patient already presented indolent lung lesions from 5 months before and he remained completely asymptomatic until the aspergillosis diagnosis when he quickly passed away. Even if a progression of the lesions was expected in 5 months, this case had an atypical presentation. During the 5-month period, he had no pulmonary symptoms, and his c-reactive protein was negative. Furthermore, in the setting of the natural progression of subacute/chronic aspergillosis, a different radiological picture was expected with a less severe and probably asynchronous evolution. We think that the immune restoration associated with Mogamulizumab (also supported by the concurrent clinical response of the skin lesions) could have been detrimental in this case, exacerbating a catastrophic immune response or alternatively masquerading the clinical progression of aspergillosis. Clinicians should be aware of immune reconstitution syndromes possibly leading to fatal outcomes in immunocompromised patients starting CCR-4 antagonists. [ABSTRACT FROM AUTHOR]

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Summary: 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. [ABSTRACT FROM AUTHOR]

Mogamulizumab is a humanized antibody targeting CC chemokine receptor 4 (CCR4). This post‐marketing surveillance was conducted in Japan as a regulatory requirement from 2014 to 2020 to ensure the safety and effectiveness of mogamulizumab in patients with relapsed or refractory (r/r) CCR4‐positive peripheral T‐cell lymphoma (PTCL) or r/r cutaneous T‐cell lymphoma (CTCL). Safety and effectiveness data were collected for up to 31 weeks after treatment initiation. A total of 142 patients were registered; safety was evaluated in 136 patients. The median number of doses was 8.0 (range, 1–18). The main reasons for treatment termination were insufficient response (22.1%) and adverse events (13.2%). The frequency of any grade adverse drug reaction was 57.4%, including skin disorders (26.5%), infections and immune system disorders (16.2%), and infusion‐related reactions (13.2%). Graft‐versus‐host disease, grade 2, developed in one of two patients who underwent allogeneic‐hematopoietic stem cell transplantation after receiving mogamulizumab. Effectiveness was evaluated in 131 patients (103 with PTCL; 28 with CTCL). The best overall response rate was 45.8% (PTCL, 47.6%; CTCL, 39.3%). At week 31, the survival rate was 69.0% (95% confidence interval, 59.8%–76.5%) [PTCL, 64.4% (54.0%–73.0%); CTCL, 90.5% (67.0%–97.5%)]. Safety and effectiveness were comparable between patients <70 and ≥ 70 years old and between those with relapsed and refractory disease. The safety and effectiveness of mogamulizumab for PTCL and CTCL in the real world were comparable with the data reported in previous clinical trials. Clinical Trial Registration [ABSTRACT FROM AUTHOR]

Human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic neurodegenerative disease. This multicenter, randomized phase 3 study evaluated the efficacy and safety of 0.3 mg/kg intravenous mogamulizumab, a monoclonal antibody targeting-CC chemokine receptor 4, every 12 weeks in HAM/TSP patients. This study comprised a 24-week double-blind, placebo-controlled period, 24-week open-label period, and extension treatment period. The primary endpoint was the proportion of patients with a ≥ 1-grade improvement in the Osame motor disability score (OMDS). Secondary endpoints were changes in HTLV-1 proviral load, 10-m timed walk, cerebrospinal fluid (CSF) neopterin levels, and safety. The exploratory endpoint was CSF chemokine C-X-C motif ligand 10 (CXCL10) levels. Thirty-four and 33 patients were randomized to mogamulizumab and placebo arms, respectively. At the end of the double-blind period, no significant difference was found in the OMDS improvement rate or other secondary efficacy endpoints assessing motor activities. However, the mogamulizumab arm showed a significant decrease in HTLV-1 proviral load (− 59.39 ± 29.91% vs. placebo 2.32 ± 36.31%) and CSF neopterin (p < 0.001)/CXCL10 levels (p = 0.004). The baseline OMDS pattern and the 60–80% HTLV-1 proviral load reduction were sustained through the open-label and extension treatment periods. Although a higher incidence of rash (69.2%) was reported, the safety profile was similar compared with a previous phase 1/2a study. We found no significant difference in clinical benefit; however, mogamulizumab may provide long-term clinical benefit by preventing disease progression, as CSF neopterin/CXCL10 levels are associated with long-term prognosis in HAM/TSP. Clinical Trial Registration Number: NCT03191526 (registered date: 6-June-2017). [ABSTRACT FROM AUTHOR]

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important therapy for patients with T-cell lymphomas, including cutaneous T-cell lymphoma (CTCL), adult T-cell lymphoma (ATL), and peripheral T-cell lymphoma (PTCL). Mogamulizumab is an anti-CCR4 antibody that has been associated with an increased risk of transplant-related complications in retrospective analyses of ATL, particularly when administered within 50 days before transplantation. This post hoc analysis of 3 clinical trials examined safety and outcome data for 32 patients with CTCL (n = 23), ATL (n = 7), or PTCL (n = 2) who underwent allo-HSCT after mogamulizumab treatment. Overall, 22 patients (69%) were known to have graft-versus-host disease (GVHD), 8 patients (25%) did not report GVHD, and 2 patients (6%) had unknown GVHD status. Fourteen patients with known GVHD underwent transplantation between 50 and 365 days after their last dose of mogamulizumab, while 2 underwent transplantation within 50 days after treatment. Based on this limited evidence, GVHD was not associated with the time interval from last mogamulizumab dose to transplantation. [ABSTRACT FROM AUTHOR]

Current treatment guidelines for cutaneous T cell lymphoma (CTCL) advocate a stage-driven approach, considering clinical presentation, symptom burden, and patient comorbidities. Therapy selection hinges on factors like disease subtype, severity, and treatment availability. The primary goal is to enhance the quality of life by mitigating symptoms, as achieving lasting complete remission is infrequent. Over the past decade (2013–2023), the therapeutic landscape of CTCL has experienced substantial transformation with the introduction of innovative therapies. This review explores the main pivotal developments in traditional treatment schedules and recently introduced drugs, aiming to offer clinicians and researchers a thorough perspective on the decade's progress in the field. Despite the progress made in CTCL therapeutics, ranging from topical chemotherapeutics to immunomodulatory agents, several unmet needs persist. Firstly, there is a pressing need for the incorporation of readily available predictors for treatment response, encompassing clinical, pathological, and molecular features. Secondly, a more profound comprehension of the tumor microenvironment is imperative to optimize the landscape of targetable molecules. Lastly, the undertaking of studies on combination regimens should be encouraged as it enhances therapy efficacies by synergistically combining agents with diverse modes of action. [ABSTRACT FROM AUTHOR]

Abstract is missing (Short communication)

Summary: Background: Sézary syndrome is an extremely rare and fatal cutaneous T-cell lymphoma (CTCL). Mogamulizumab, an anti-CCR4 monoclonal antibody, has recently been associated with increased progression-free survival in a randomized clinical trial in CTCL. We aimed to evaluate OS and prognostic factors in Sézary syndrome, including treatment with mogamulizumab, in a real-life setting. Methods: Data from patients with Sézary (ISCL/EORTC stage IV) and pre-Sézary (stage IIIB) syndrome diagnosed from 2000 to 2020 were obtained from 24 centers in Europe. Age, disease stage, plasma lactate dehydrogenases levels, blood eosinophilia at diagnosis, large-cell transformation and treatment received were analyzed in a multivariable Cox proportional hazard ratio model. This study has been registered in ClinicalTrials (SURPASSe01 study: NCT05206045). Findings: Three hundred and thirty-nine patients were included (58% men, median age at diagnosis of 70 years, Q1-Q3, 61–79): 33 pre-Sézary (9.7% of 339), 296 Sézary syndrome (87.3%), of whom 10 (2.9%) had large-cell transformation. One hundred and ten patients received mogamulizumab. Median follow-up was 58 months (95% confidence interval [CI], 53–68). OS was 46.5% (95% CI, 40.6%–53.3%) at 5 years. Multivariable analysis showed that age ≥ 80 versus

Mogamulizumab (MOG) is an antibody targeting the CCR4 receptor, authorized for relapsed or refractory peripheral T-cell (PTCL) and cutaneous T-cell lymphomas (CTCL). Its adoption in guidelines and endorsement by FDA and EMA established it as a systemic treatment, especially for advanced disease stages due to its comparatively lower toxicity. Clinical trials and real-world evidence have underscored its efficacy in advanced CTCLs, including mycosis fungoides and Sézary syndrome; PTCLs; and adult T-cell leukemia/lymphoma (ATLL), showcasing positive outcomes. Notably, the drug has demonstrated significant response rates, disease stability, and extended periods of progression-free survival, suggesting its applicability in cases with multiple treatment lines. Its safety profile is generally manageable, with adverse events (AEs) primarily related to the skin, infusion-related reactions, drug eruptions, autoimmune diseases, and skin disorders. The latter seem to appear as CCR4 can promote the skin-specific homing of lymphocytes, and MOG is directed against this receptor. While combination with immunostimulatory agents like interferon alpha and interleukin 12 has shown promising results, caution is urged when combining with PD1 inhibitors due to the heightened risk of immune-mediated AEs. The introduction of MOG as a systemic treatment implies a significant advancement in managing these diseases, supported by its favorable safety profile and complementary mechanisms. [ABSTRACT FROM AUTHOR]

Simple Summary: Cutaneous T-cell lymphomas (CTCLs) constitute a group of rare lymphoproliferative malignancies primarily manifesting in the skin. This study aimed to assess a combined treatment approach utilizing mogamulizumab and extracorporeal photopheresis for a subset of patients in an advanced stage of this disease, which typically challenges therapy and carries an unfavorable prognosis. The present study aimed to understand the impact of this novel treatment combination on skin- and blood-related symptoms and its associated side effects. This retrospective study included 11 patients with Sézary syndrome (SS) or mycosis fungoides (MF). Encouragingly, three-fourths of the patients showed positive responses, with improvements in skin-related symptoms, a decrease in malignant cells in the blood, and a minimum progression-free survival of 7.2 in the skin and 7.6 months in the blood. Overall, the treatment demonstrated good tolerance. If confirmed through larger-scale studies, this combined therapy could potentially establish a new therapeutic option for patients with advanced-stage cutaneous T-cell lymphoma. Background: Primary cutaneous T-cell lymphomas (CTCLs) are rare lymphoproliferative malignancies characterized by significant morbidity and mortality in advanced disease stages. As curative approaches apart from allogeneic stem cell transplantation are lacking, establishing new treatment options, especially combination therapies, is crucial. Methods: This retrospective study included 11 patients with SS or MF receiving therapy with mogamulizumab in combination with ECP from four European expert centers. The response rates in the skin and blood as well as treatment use and adverse events (AE) were described. Results: 8/11 patients (73%) showed an overall response (OR) in the skin. The mean mSWAT decreased from 98.2 ± 40.8 to 34.6 ± 23.8. The overall response rate (ORR) in the blood was 64% with two complete responses. During combination therapy, the mean number of Sézary cells decreased from 3365.3 × 106/L before treatment to 1268.6 × 106/L. The mean minimum known period without progress was 7.2 months in the skin and 7.6 months in the blood. The most common AEs were mogamulizumab-associated rash (MAR) (45.5%), anemia (27.3%), lymphocytopenia (27.8%), and infusion related reaction (16.7%). No AE led to treatment discontinuation. Conclusions: Our study presents the combination of mogamulizumab and ECP as an effective therapy in the blood and skin in CTCL with good tolerability, similar to mogamulizumab monotherapy. [ABSTRACT FROM AUTHOR]

Cutaneous T-cell lymphomas are a diverse group of T-cell neoplasms, characterised by initial infiltration of the skin, and sometimes extension to the lymph nodes, blood and internal organs. Sézary syndrome is an erythrodermic form distinguished by the significant presence of circulating peripheral blood tumour cells. Numerous diagnostic and therapeutic advances have been made in this disease in recent years, and we offer here a non-exhaustive review. [ABSTRACT FROM AUTHOR]

Treatment with CCR-4 antagonists has been shown to be protective against the development of invasive pulmonary aspergillosis in animal models. Herein, we present a case of fatal invasive pulmonary aspergillosis in a patient receiving Mogamulizumab. A 64-year-old man with refractory mycosis fungoides was found to have diffuse bilateral pulmonary nodules during a chest CT in June 2022. Bronchoalveolar lavage (BAL) fungal and bacterial cultures and galactomannan were negative, as well as serum beta-glucan and galactomannan. Histology showed a lymphoid infiltrate with a negative fungal stain, so a presumptive diagnosis of lymphoma infiltration was made, and the patient started the CCR-4 antagonist Mogamulizumab treatment in August 2022. He had no symptoms until November when he presented to the hematology clinic reporting dyspnea. He had neutrophilic leukocytosis (18.610 cells/µL), his c-reactive protein was 27 mg/dL, and his skin lesions from mycosis fungoides were just starting to improve. A CT scan showed large diffuse bilateral severely necrotic cavitated lesions with thick walls and apparently synchronous evolution. Beta-glucan was 31 pg/mL (wako method), while serum galactomannan 3.6. BAL was positive for Aspergillus fumigatus culture and galactomannan. Patient started voriconazole but, despite being in a stable condition, he suddenly died after two days. Discussion: Paradoxically, worsening of the chronic pulmonary aspergillosis has been reported after nivolumab treatment, and immune reconstitution syndromes are usually seen during neutrophil recovery after intensive chemotherapy. Our patient already presented indolent lung lesions from 5 months before and he remained completely asymptomatic until the aspergillosis diagnosis when he quickly passed away. Even if a progression of the lesions was expected in 5 months, this case had an atypical presentation. During the 5-month period, he had no pulmonary symptoms, and his c-reactive protein was negative. Furthermore, in the setting of the natural progression of subacute/chronic aspergillosis, a different radiological picture was expected with a less severe and probably asynchronous evolution. We think that the immune restoration associated with Mogamulizumab (also supported by the concurrent clinical response of the skin lesions) could have been detrimental in this case, exacerbating a catastrophic immune response or alternatively masquerading the clinical progression of aspergillosis. Clinicians should be aware of immune reconstitution syndromes possibly leading to fatal outcomes in immunocompromised patients starting CCR-4 antagonists.

Topical chlormethine gel has been approved as monotherapy for treatment of adult patients with mycosis fungoides (MF), the most common form of cutaneous T-cell lymphoma. In clinical practice, chlormethine gel is often combined with other skin-directed or systemic therapies to optimize response and target recalcitrant lesions. Positive outcomes with combination regimens using chlormethine gel and topical corticosteroids, phototherapy, retinoids, methotrexate, or interferon-α have been reported in literature. However, there are no treatment guidelines on the use of combination regimens with chlormethine gel. To provide real-world evidence and guidance on the use of chlormethine gel combination regimens, several cases of patients treated with chlormethine gel combined with phototherapy (n = 5), retinoids (n = 16), or mogamulizumab (n = 3) are presented. These different combination regimens showed promising results. Most patients had a complete or partial response following treatment and the combinations were well-tolerated over extended treatment periods. Patients receiving chlormethine gel with retinoids had long-term periods of remission, even after treatment discontinuation. Durations of response of up to 3 years were observed in these patients. This long-term disease control may be the result of disease-modifying effects of chlormethine. Previous studies have shown targeted reductions in malignant T-cell clones in patients treated with chlormethine gel as well as improved post-treatment responses. Further research is needed to determine the effectiveness and safety of combination treatment regimens with chlormethine gel and to assess the impact chlormethine gel has on disease control.

Cutaneous adverse events of both topical and systemic drugs in patients with mycosis fungoides (MF) present a diagnostic challenge as it is often difficult to distinguish drug associated rash from disease progression in the skin. Mogamulizumab and mechlorethamine gel are approved treatments for MF, both of which can cause treatment related cutaneous adverse events. It can often be challenging to distinguish mogamulizumab associated rash (MAR) and mechlorethamine gel associated hypersensitivity dermatitis from MF progression both clinically and histologically. High-throughput sequencing (HTS) of the T-cell receptor (TCR), also known as immunosequencing, can be used to assess T-cell clonality to support a diagnosis of MF. After identification of the malignant TCR clone at baseline, immunosequencing can track the established malignant TCR sequence and its frequency over time with high sensitivity. As a result, immunosequencing clone tracking can aid in distinguishing disease progression from treatment side effects. Here, we present a case series to demonstrate how monitoring of the malignant T-cell frequency by immunosequencing can aid in diagnosis of mogamulizumab and mechlorethamine gel cutaneous adverse events.