SMARCB1/INI1-deficient lung cancer with lymph node metastasis: a case report and literature review.

Background: Switch/Sucrose non-fermentable-related, matrix-associated, actin-dependent regulator of chromatin subfamily B member 1/integrase interactor 1 (SMARCB1/INI1)-deficient lung cancer is a very rare and highly invasive malignant tumor, of which clinicians and pathologists often have limited understanding.

Case description: We present a 54-year-old man with SMARCB1/INI1-deficient lung cancer, pathologically confirmed by computed tomography guided percutaneous pulmonary mass biopsy and ultrasound-guided lymph node biopsy. Both lymphoids and lung tissues showed INI1 deletion and high Ki-67 index; next generation sequencing (NGS) indicated a tumor protein 53 (TP53) mutation abundance of 22.18% and cyclin-dependent kinase 4 (CDK4) amplification (copy number of 4.30). Currently, SMARCB1/INI1-deficient lung cancer is rare, and no standardized treatment plan is available, and there was no clear and effective targeted drug. Considering the high expression of programmed cell death ligand 1 (PD-L1), the patient was advised to undergo treatment with anti-programmed cell death 1 (PD-1) immune checkpoint inhibitors. Unfortunately, because the patient and his family have low financial resources, only afford resident insurance and cannot afford follow-up medical expenses, the patient refused treatment and passed away 3 months after diagnosis.

Conclusions: We provided the clinical symptoms, imaging data, and literature findings of this rare case of SMARCB1/INI1-deficient lung cancer with lymph node metastasis as a reference, hoping to help clinicians and pathologists have a better understanding of it and avoid misdiagnosis.