Durable benefit from immunotherapy and accompanied lupus erythematosus in pancreatic adenocarcinoma with DNA repair deficiency

BACKGROUND: Clinical trials showed limited benefit of anti-PD-1 (programmed cell death 1) monotherapy in pancreatic adenocarcinoma patients and immune-related adverse events caused by immune checkpoint inhibitors were rarely reported in pancreatic adenocarcinoma. Here, we report the first case of durable benefit along with systemic lupus erythematosus following immunotherapy in mismatch repair-proficient pancreatic cancer. CASE PRESENTATION: We describe a 57-year-old woman with resected stage ⅢB pancreatic cancer who underwent several lines of conventional chemotherapy after multiple lymph node metastases. When the disease progressed again, the patient received an off-label treatment with pembrolizumab (100 mg every 3 weeks). After four cycles of immunotherapy treatment, CA19-9 level rapidly decreased to normal and the lymph node metastases reduced dramatically in volume, demonstrating a partial response to the therapy by RECIST 1.1 criteria. She continued on pembrolizumab and a total of eight cycles of administration she had received. Her lesions showed consistent reduction in size even when the medication had been stopped. Actually the patient experienced durable benefit from anti-PD-1 therapy for more than 4 years and she is still in good condition without tumor relapses to date. Besides, she was diagnosed with systemic lupus erythematosus 2 months after the last dose of pembrolizumab. Molecular profiling identified two deleterious PALB2 alterations including a germline mutation (PALB2 c.3114–1G>A) and a somatic mutation (PALB2 c.2514+1G>C) in this patient, suggesting the potential of DNA homologous recombination deficiency. Multiplex immunohistochemistry and RNA-seq results revealed a brisk immune cell infiltration in her resected primary lesion. Additionally, humanleukocyte antigen (HLA) typing assay identified two previously reported systemic lupus erythematosus risk alleles HLA-DRB1*15:01 and HLA-DQB1*06:02 in this patient. CONCLUSIONS: The deleterious mutations of PALB2 closely related to homologous recombination deficiency or alterations of DNA damage response and repair genes might be promising biomarkers for predicting efficacy of immune checkpoint inhibitors in pancreatic adenocarcinoma. Genetic correlation behind immunotherapy-induced systemic lupus erythematosus and associated mechanism remain to be elucidated.