Late Breaking Abstract – ASCO 2015 KEYTRUDA®, an Anti PD-1 Antibody for Advanced Head and Neck Cancer

SUMMARY: The American Cancer Society estimates that 59,340 people will be diagnosed with Head and Neck cancer in 2015 and 12,290 patients will die of the disease. Patients with recurrent/metastatic Squamous Cell Carcinoma of the Head and Neck (SCCHN) have a poor prognosis with a median Overall Survival (OS) of about 13 months with first line therapy and about 6 months or less with later lines of therapy. The treatment paradigm for solid tumors has been rapidly evolving with a better understanding of the Immune checkpoints. Immune checkpoints are cell surface inhibitory proteins/receptors that are expressed on activated T cells. They 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 therefore play a very important role in modulating the immune system. Under normal circumstances, inhibition of an intense immune response and 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. KEYTRUDA® (Pembrolizumab) is a fully humanized, Immunoglobulin G4, monoclonal antibody, that binds to the PD-1 receptor and blocks its interaction with ligands PD-L1 and PD-L2, thereby undoing PD-1 pathway-mediated inhibition of the immune response and unleashing the tumor-specific effector T cells. The FDA granted accelerated approval to KEYTRUDA® in September 2014, for the treatment of patients with unresectable or metastatic melanoma and disease progression following YERVOY® and, if BRAF V600 mutation positive, a BRAF inhibitor. The activity of KEYTRUDA® as a single agent in advanced SCCHN patients, was previously published and was noted in PD-L1 positive tumors, regardless of the Human PapillomaVirus (HPV) status. The Overall Response Rate in this patient group was 20% and 29% of patients had stable disease. The authors in this study reported the efficacy of once every three week dose of KEYTRUDA®, in a larger expansion cohort of KEYNOTE 012 study. In this study, 132 patients with recurrent/metastatic SCCHN were enrolled, regardless of their PD-L1 expression or HPV status. These patients received a fixed dose of KEYTRUDA® 200 mg IV, every 3 weeks and patients were evaluated every 8 weeks with radiographic imaging. The mean age was 59 years and 57% of the patients had 2 or more lines of therapy for recurrent disease. Treatment was continued until disease progression. The primary end point was Overall Response Rate (ORR) and secondary endpoints included Progression Free Survival (PFS) and Overall Survival (OS). The Overall Response Rate was 25% and stable disease was noted in an additional 25% of the patients. This amounted to a disease control rate of 50%. Patients with HPV-positive disease had a response rate of 20.6% and patients with HPV-negative disease had a response rate of 27.2%, suggesting that KEYTRUDA® was active in both subgroups of patients. Serious toxicities were reported in fewer than 10% of patients and the most common adverse event was fatigue (15.2%). The authors concluded that KEYTRUDA® given every 3 weeks was well tolerated and demonstrated a meaningful response rate in a heavily pretreated population of patients, with recurrent/metastatic SCCHN. Evaluation of PD-L1 status for this patient group is ongoing. Antitumor activity and safety of pembrolizumab in patients (pts) with advanced squamous cell carcinoma of the head and neck (SCCHN): Preliminary results from KEYNOTE-012 expansion cohort. Seiwert TY, Haddad RI, Gupta S, et al. J Clin Oncol 33, 2015 (suppl; abstr LBA6008)</s