SUMMARY: It is estimated that in the US, approximately 76,000 new cases of melanoma will be diagnosed and close to 8000 individuals will die of the disease in 2014. The incidence of melanoma has been on the rise for the past three decades. Unlike other malignancies, the role of chemotherapy for the treatment of melanoma has been limited. Treatment of advanced melanoma with immunotherapy using a cytokine, Interleukin-2 (IL-2) produced by T cells during an immune response, was first explored in the mid 1970’s. Durable responses were noted in a very small percentage of patients but this was associated with significant toxicities. This however opened the doors for the development of various immunotherapies, with a better understanding of the Immune checkpoints. Immune checkpoints are cell surface inhibitory proteins/receptors that harness the immune system and prevent uncontrolled immune reactions. Survival of cancer cells in the human body may be to a significant extent, related to their ability to escape immune surveillance, by inhibiting T lymphocyte activation. The T cells of the immune system play a very important role in modulating the immune system. Under normal circumstances, inhibition of an intense immune response, by switching off the T cells of the immune system, is an evolutionary mechanism and is accomplished by Immune checkpoints or Gate Keepers. With the recognition of Immune checkpoint proteins and their role in suppressing antitumor immunity, antibodies are being developed that target the membrane bound inhibitory Immune checkpoint proteins/receptors such as CTLA-4 (Cytotoxic T-Lymphocyte Antigen 4, also known as CD152), PD-1 (Programmed cell Death-1), etc. By doing so, one would expect to unleash the T cells, resulting in T cell proliferation, activation and a therapeutic response. The first immune checkpoint protein to be clinically targeted was CTLA-4. YERVOY® (Ipilimumab), an antibody that blocks Immune checkpoint protein/receptor CTLA- 4, has been shown to prolong overall survival in patients with previously treated, unresectable or metastatic melanoma.
The Food and Drug Administration in May 2014, granted Pembrolizumab a Priority Review designation under its Accelerated Approval Program. Pembrolizumab was previously granted a Breakthrough Therapy designation for advanced melanoma. The authors in this largest phase I clinical trial ever done in patients with malignant melanoma, evaluated the efficacy and safety of Pembrolizumab (formerly known as MK-3475, Lambrolizumab), a humanized monoclonal IgG4 anti PD-1 antibody, in a pooled analysis of 411 patients with advanced melanoma. Of these patients, 221 patients had prior therapy with Ipilimumab (YERVOY® ) and 190 patients were YERVOY® naïve. In this study, three different dosing schedules for Pembrolizumab were utilized – 2 mg/kg every three weeks (N=162), 10 mg/kg every three weeks (N=192) and 10 mg/kg every two weeks (N=57). At the time of this analysis, all patients had at least 6 months of follow up and 75% of the patients had been followed up for at least 9 months. The Overall Response Rate was 40% in the YERVOY® naïve group and 28% in the YERVOY® treated group. Responses were durable and ongoing (88% ongoing) at the time of this analysis. The duration of responses ranged from 6 to 76 weeks, and the median response duration has not yet been reached. The median Progression Free Survival was 24 weeks in YERVOY® naïve group and 23 weeks in the YERVOY® treated group. The median Overall Survival has not been reached at the time of this analysis and the estimated 1 year Overall Survival rate for all patients was 71%. The activity with Pembrolizumab was demonstrated across all dose levels and patient subgroups, irrespective of prior YERVOY® therapy, performance status, LDH levels, BRAF mutation status, tumor stage, and number, as well as type of prior therapies. The most common adverse events of any grade were fatigue, pruritus and rash. Only 4% of the patients discontinued treatment due to a drug related toxicities and overall, 12% of patients experienced grade 3/4 adverse events. The authors concluded that the PD-1 targeting antibody, Pembrolizumab, produced durable responses in patients with advanced melanoma, regardless of prior therapy with YERVOY® and this benefit was accomplished with minimal toxicities. This efficacy data is comparable to another PD-1 targeted monoclonal antibody, Nivolumab. Because of the lack of cross resistance between anti PD-1 antibodies and YERVOY®, combining PD-1 targeted monoclonal antibody with a CTLA-4 targeted antibody such as YERVOY®, could potentially be synergistic, with better outcomes. Ribas A, Hodi FS, Kefford R, et al. J Clin Oncol 32:5s, 2014 (suppl; abstr LBA 9000)</s
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