Tailing effect of PD-1 antibody results in the eradication of unresectable multiple primary lung cancer presenting as ground-glass opacities: a case report.

There is currently no standard treatment for multiple primary lung cancer (MPLC). We report a case of synchronous MPLC presenting as one ground-glass opacity (GGO) with predominant consolidation accompanied by at least parietal pleura involvement, and another with >30 GGOs distributed across bilateral lungs, which was ineligible for complete resection. CT-guided percutaneous biopsy of the nearly pure-solid mass showed invasive lung adenocarcinoma mainly composed of acinar type. Capture-based, ultra-deep targeted sequencing (Burning Rock, Guangzhou, China) was performed on the tumor tissue biopsy. The result revealed no druggable mutations according to the guideline and a high TMB of 34.1 Mb. Immunohistochemical staining (22C3; Dako, Denmark) was positive for PD-L1 expression with a tumor expression level of 30%. Based on the clinical information and patient's decision, he received 3 cycles of pemetrexed plus pembrolizumab and was subsequently forced to withdraw due to acquired immune-related pneumonitis. After discontinuation of corticosteroids, he was subjected to wedge resection for the nearly pure-solid lesion, and then refused further treatment for the other tumors. After a follow-up of 12 months from termination of immunotherapy, almost all GGOs achieved radiographically complete remission, attributed to the tailing effect of the programmed cell death protein 1 (PD-1) antibody of pembrolizumab. Through the case study we found that unresectable synchronous MPLC presenting as GGOs may respond well to immunotherapy.