Lower dose pembrolizumab monotherapy in the treatment of brain metastases from non-small cell lung carcinoma: A report of two cases

Abstract

Introduction: Lung cancer is the leading malignancy metastatic to the central nervous system with
approximately 20% to 44% of all cases developing brain metastasis. Immunotherapy using pembrolizumab,
an anti-PD1monoclonal antibody, is a novel method in lung cancer treatment and has shown favorable results
in patients with metastatic brain lesions from non-small cell lung carcinoma (NSCLC). However, the cost of the recommended treatment dose limits its use especially in developing countries like the Philippines.

Case Presentation:  The authors report two patients with lung cancer with brain metastasis upon diagnosis.
The first patient is a 65-year-old male, non-smoker with PD-L1 expression of 60%. He was started on
pembrolizumab 100 mg IV every three (3) weeks and a repeat CT scan after 11 cycles revealed a reduction of the two brain metastatic lesions and no fluoro-D-glucose (FDG) uptake on positron emission tomography
(PET) scan even after one year into treatment. The second patient is a 67-year-old female, a previous smoker with PD-L1 expression of 50% with a metastatic solitary solid nodule in the cortex of the right cerebellum. After five cycles of pembrolizumab 100 mg IV every three weeks, there was noted complete resolution of brain metastasis on PET scan even after one year of treatment.

Conclusion: A lower dose of pembrolizumab (100 mg given every 3 weeks) was found to be effective in the
management of advanced NSCLC with brain metastasis in the two patients. Further studies are recommended
to investigate lower dose pembrolizumab as monotherapy without radiation therapy or surgery in patients
with NSCLC with brain metastasis especially in the setting of a resource-limited country like the Philippines.