Pembrolizumab is a humanized IgG4 Kappa monoclonal programmed death receptor 1 directed antibody FDA approved for the first line treatment of metastatic non-small cell lung carcinoma (NSCLC) expressing >=50% PD-L1. Pseudoprogression in this context has rarely been reported. We encountered a patient within our community practice who received treatment with pembrolizumab and demonstrated radiologic features of pseudoprogression initially followed by clinical progression where upon histologic evaluation favored pseudoprogression over progression. The aims of this study are as follows: Firstly, to describe the clinico-pathologic-radiologic aspects of this patient’s treatment journey; secondly, to histologically characterize a lesion that was biopsied which showed clinical features of progression, but histologically, pseudoprogression; thirdly, to perform detailed flow cytometric analysis of lymphocytes obtained through the biopsy to characterize pseudoprogression. This is a single patient case study performed by reviewing clinical notes, radiology, and histology. Samples obtained on biopsy were further characterized by flow cytometry. A 72-year-old male patient with small volume metastatic squamous cell lung carcinoma with a tumor proportion score of 100% for PD-L1, was initially treated with radiation (20Gy) to palliate worsening dyspnea caused by airway obstruction. He had good local control with improvement in dyspnea and subsequently requested for observation only. Serial imaging revealed the development of an abdominal wall nodule. Before long, his metastatic disease became symptomatic and he was treated with first line pembrolizumab. Three weeks after his first dose, he presented with severe abdominal wall pain and a new palpable abdominal wall mass. Imaging performed confirmed the presence of a new abdominal wall mass in contrast to a reduction in size of his pulmonary lesions. This was thus assessed as pseudoprogression, and he was continued on treatment with radiologic response noted three weeks later in all lesions. He discontinued treatment due to cost at this point, and subsequently restarted treatment upon radiologic progression of disease. On restarting treatment, his abdominal wall nodule increased in size and ulcerated. True tumor progression was considered prompting biopsy of the abdominal wall nodule to enable stratification into clinical trials. However, histologic evaluation showed chronically inflamed granulation tissue with no microscopic evidence of malignancy suggesting pseudoprogression once again instead. The patient went on to receive radiotherapy to the abdominal wall nodule, and a serial scan demonstrated a reduction in size of the abdominal wall nodule and stable pulmonary disease. Flow cytometric analysis of biopsy tissue revealed predominantly CD45+ cells, 69.5% of which were CD3+. CD45+CD3+CD56- cells comprised CD4+ (27.9%), CD8+ (64.9%), CD4+PD1+ (46.7%), CD8+PD+ (37.7%). Further analysis by flow and mass cytometry is ongoing, and attempts are also being made to assess the tumor antigen specificity of the T-cells. In a patient with clinically immunogenic cancer responding to intermittent anti-PD1 therapy, we observed varying clinico-radiologic responses across his metastatic lesions, and a pathologic evaluation of a clinically progressing lesion revealed pseudoprogression instead.

Citation Format: Tiffany Hennedige, Daniel Tan, Narayanan Gopalakrishna Iyer, Amit Jain. Pseudoprogression of metastatic abdominal wall nodules in a patient with lung carcinoma treated with pembrolizumab [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B161.