PD-L1 induction in tumor tissue after hypofractionated thoracic radiotherapy for non-small cell lung cancer.

We report on a 67-year old male with advanced stage lung adenocarcinoma (initially PD-L1 negative, EGFR and ALK negative) diagnosed in 2014. The patient received 4 lines of palliative chemotherapy from 2014 to 2017, however the disease progressed. In 2015, he also received palliative hypofractionated radiotherapy to a mediastinal mass, which was causing discomfort and pain. Since there was some data, that radiotherapy could induce PD-L1 expression, a new biopsy was taken in 2017 from the irradiated mediastinal mass. Subsequent pathologic report revealed that PD-L1 status was turned to be highly positive, with tumor proportion score of 100%. Similar high expression of PD-L1 was detected in a new metastasis in the duodenum, which was excised due to a duodenal perforation in 2017. From October 2017 to October 2019, the patient had 2-years of treatment (32 courses) with pembrolizumab and has had a positive effect (partial response) on all the lesions and following stabilization of the disease. Currently, this patient is under follow up and he is in a good condition without any complaints. Last CT-scan in March 2020 showed persisting partial response.