From 1st November 2018, pembrolizumab is available on the Pharmaceutical Benefits Scheme (PBS) for the first-line treatment of metastatic non-small cell lung cancer. This is in addition to its original listing for Stage III or IV malignant melanoma and relapsed or refractory Hodgkin lymphoma.

Pembrolizumab, known as a checkpoint inhibitor, is a humanised monoclonal antibody with high affinity for the programmed death 1 (PD-1) receptor. Activation of this receptor with programmed death ligand 1 and 2 (PD-L1 and PD-L2) may assist tumours to evade T-cell immunologic responses. Pembrolizumab blocks this receptor, enhancing the host’s immune response to the cancer by reactivating tumour-specific cytotoxic T cells.

The KEYNOTE-024 trial investigated the efficacy of pembrolizumab in patients with non-small cell lung cancer and high levels of PD-L1 expression, defined as a tumour proportion score (TPS) of at least 50%. Pembrolizumab was associated with a significantly longer progression-free survival (10.3 versus 6.0 months) and overall survival at six months (80.2% versus 72.4%) compared to platinum-based chemotherapy. Up to 28% of patients with non-small cell lung cancer are thought to have a TPS of at least 50%; studies demonstrate that patients with lower expression are less likely to benefit.

The incidence of treatment-related adverse events was lower in the pembrolizumab group at 73.4%, compared to 90.0% of patients in the chemotherapy group. More serious adverse events (grade 3 or above) were reported twice as frequently in the chemotherapy group. The most common adverse events of a grade 1 or 2 severity reported in the pembrolizumab group were diarrhoea, fatigue, and pyrexia. More serious adverse events included diarrhoea, pneumonitis, and severe skin reactions.

This new PBS listing means that eligible patients can avoid chemotherapy. Nivolumab, another PD-L1 inhibitor PBS listed for non-small cell lung cancer, is reserved for patients who have progressed on or after prior chemotherapy.

References:

  1. Gong J, Chehrazi-Raffle A, Reddi S, Salgia R. Development of PD-1 and PD-L1 inhibitors as a form of cancer immunotherapy: a comprehensive review of registration trials and future considerations. J Immunother Cancer. 2018; 6:8.
  2. Keytruda® (pembrolizumab) Australian approved product information. Macquarie Park: Merck Sharp & Dohme. Approved October 2018.
  3. Reck M, Rodríguez-Abreu D, Robinson AG, Hui R, Csőszi T, Fülöp A, et al. Pembrolizumab versus chemotherapy for PD-L1–positive non–small-cell lung cancer. N Engl J Med. 2016; 375: 1823-33.

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