Occult SMARCA4-Deficient Undifferentiated Carcinoma Unmasked by 68Ga-FAPI-46 PET/CT

SMARCA4-deficient undifferentiated tumors (SMARCA4-dUT) are rare and aggressive neoplasms commonly found in male smokers and portend a poor prognosis. In this case, we reported 18F-FDG and 68Ga-FAPI-46 PET/CT findings in an occult SMARCA4-dUT located in the left pulmonary hilum along with mediastinal lymph node metastases. 68Ga-FAPI-46 PET/CT showed superiority over 18F-FDG for detecting SMARCA4-dUT lesions. This case highlighted that 68Ga-FAPI-46 PET/CT may be a promising imaging modality in the evaluation of SMARCA4-dUT, particularly for detecting the occult SMARCA4-dUT arising in uncommon sites.