Keeping Mycosis Fungoides in Check: A Study of Pembrolizumab for Relapsed/Refractory MF and Sezary Syndrome

This podcast evaluates results from a phase II clinical trial of pembrolizumab for relapsed Mycosis Fungoides and Sezary Syndrome in the context of the current systemic treatment landscape for this disease. TRANSCRIPT This JCO Podcast provides observations and commentary on the JCO article "Pembrolizumab in Relapsed and Refractory Mycosis Fungoides and Sezary Syndrome: A Multicenter Phase II Study" by Khodadoust et al. My name is Jennifer Amengual, and I am an Assistant Professor of Medicine at the Columbia University Irving Medical Center in New York, New York, USA. My oncologic specialty is lymphoma. Mycosis fungoides, otherwise known as MF, and Sezary Syndrome, its leukemic variant, are rare subtypes of cutaneous T-cell lymphoma. Although most patients with MF have indolent disease, those with advanced stage MF often experience resistance to systemic therapy with a persistent and progressive disease course, which has a negative impact on overall well-being and survival. Patients may have intense pruritus, which can then put them at increased risk for staphylococcus infection, sepsis and in turn can trigger disease flare. Advanced-stage MF is a chronic disease that is not considered curable; therefore, it is necessary to consider management strategies that provide symptom relief and can be maintained over a long period of time. Most patients cycle through a multitude of therapies, often including skin-directed and, later, systemic therapies. Many of the acceptable therapies are derived from retrospective studies or single-arm trials; therefore, it is not possible to objectively compare outcomes and toxicity. In order to put the outcomes of pembrolizumab in context of other acceptable treatment modalities, I will discuss some of these treatments now. Systemic retinoids, such as bexarotene, are taken orally and can induce an overall response of 45-55%. The drug is well tolerated but can lead to hypertriglyceridemia and hypothyroidism, requiring monthly monitoring and frequent treatment with lipid-lowering agents and thyroid hormone replacement. Low-dose methotrexate, administered either orally or by intravenous infusion weekly, can lead to response rates between 30 and 50%. Common side-effects include mucositis, cytopenias and gastrointestinal upset. Pralatrexate is a novel antifolate drug that when studied using half the dose of that which is approved for PTCL , induced a 45% response rate for patients with MF. The treatment is also well tolerated, with the most common side-effects being mucositis and thrombocytopenia. There are 2 histone deacetylase inhibitors approved for use in MF and Sezary Syndrome. Both romidepsin and vorinostat have overlapping toxicity profiles, including gastrointestinal disturbances, fatigue, anorexia, and cytopenias. Romidepsin is also associated with ECG abnormalities. In patients with cutaneous T cell lymphoma, romidepsin has demonstrated a response rate of 34% and is associated with a median duration of response of 15 months. Vorinostat, an oral drug, has demonstrated a response rate of 30%. Recently, 2 biologics have been in used for patients with MF. Brentuximab vedotin is an antibody drug conjugate which targets the surface marker CD30 and brings monomethyl auristatin E into the cell. It is associated with a response rate of 70% in MF. Responses are significantly better in those with greater than 5% of CD30 expression. The most common side-effect is peripheral neuropathy. Mogamulizumab is a humanized antibody directed against the chemokine receptor CCR4.  This agent was studied in a randomized trial compared to vorinostat, where it led to a PFS of 7.7 months and response rate of 28%. The most common adverse events were attributed to infusion reactions, rash, diarrhea, and fatigue. There was also an increased risk of graft-versus-host disease in patients who subsequently went on to allogenic transplant, which needs to be considered when using this treatment strategy. As you can see, there are many different approaches to the treatment of advanced-stage MF and Sezary Syndrome, and the drugs I have discussed do not encompass an exhaustive list. Immune checkpoint antibodies against Programmed cell death protein 1 otherwise known as PD-1 interfere with inhibitory signaling pathways expressed on exhausted T-cells and wake up these cells allowing them to perform anti-tumor activities. The investigators rationalize the use of PD-1 inhibitors in MF and Sezary syndrome given PD-1 dysfunction and altered expression on MF cells and  the skin microenvironment. The Cancer Immunotherapy Trials Network performed a multicenter phase II single-arm study of pembrolizumab in 24 patients across 8 centers with relapsed or refractory MF or Sezary Syndrome. Of the 24 patients enrolled, 9 had MF and 15 had Sezary syndrome. Most had advanced disease represented by tumor stage disease, erythrodermic presentation, or were stage IIIB or higher. Patients received a median of 4 prior lines of systemic therapy. In addition, 4 patients had evidence of histologic large cell transformation. These represent some of the most challenging clinical situations. Pembrolizumab was administered every 3 weeks for 24 months or until withdrawal of consent, adverse reactions or investigator’s decision. The therapy was well tolerated, with no grade 4 or 5 immune-related adverse events. There were, however, 11 immune-related adverse events observed among 9 patients. This led to discontinuation of treatment in 4 patients, all due to grade 3 events including pneumonitis, duodenitis, hepatitis, and a corneal ulcer. Interestingly, over half of the patients with Sezary Syndrome experienced a flare of their symptoms early in their treatment course. This manifested as increased erythema, pruritus, and peripheral edema. Patients were managed with topical steroids and close observation. Only 1 patient had a prolonged reaction requiring systemic therapy, and no patients were discontinued from therapy due to flare of their disease. Patients with MF did not experience any skin toxicity. The authors investigated the relationship of this reaction to response and found that 3 of 8 Sezary patients who experienced a skin flare went on to achieve a response, whereas only 1 of the 7 Sezary patients who did not have a flare achieved a response. Using mass cytometry profiling of PBMCs, the authors observed a sevenfold increase in PD-1 expression on circulating Sezary cells in patients who experienced a flare. Although these observations were made across a small number of patients, it will be worthwhile to pay attention to this in future studies to determine if this is a true predictor for flare reaction or response. Pembrolizumab demonstrated significant clinical responses in 9 of 24 patients, leading to an overall response rate of 38%. This falls right into the range with other acceptable treatment options. Patients were heavily pretreated, yet the number of prior lines of therapy did not impact the response to pembrolizumab, possibly owing to non-overlapping mechanism of action. In addition, responses were seen in both MF and Sezary patients and those with erythrodermic and tumor stage presentations. There was a trend toward better outcomes in the MF patients. Responses were durable, and the median duration was not reached within a follow-up period of 58 weeks. The 1-year PFS was 65%, and OS was 95%. Two responding patients relapsed 8 to 12 weeks after discontinuation of treatment. The authors discuss that this may indicate the need for continuous treatment in this patient population, which is contrary to the general treatment strategy used for checkpoint inhibitors in other malignancies. Although this study only enrolled 24 patients, pembrolizumab appears to have similar outcomes as other drugs used in advanced-stage MF and Sezary Syndrome, with an acceptable toxicity profile. It produces a long duration of response, making it an attractive addition for patients suffering from this disease. Pembrolizumab does not have overlapping mechanism of action with most of the drugs used today and can therefore be easily integrated into the sequence of treatment for patients with MF and Sezary Syndrome. Finally, it is possible that pembrolizumab’s effects will enhance those seen with other agents. We should look forward to confirmatory clinical trials of pembrolizumab for the management of patients with MF or Sezary Syndrome. This concludes this JCO Podcast. Thank you for listening.