¹⁸F-FDG PET/CT imaging in pulmonary sarcomatoid carcinoma and correlation with clinical and genetic findings

Objective: Pulmonary sarcomatoid carcinoma (PSC) is a rare subtype of non-small-cell lung cancer with poor prognosis. This study analyzed ¹⁸F-FDG PET/CT in PSC and possible correlations with the clinical and genetic findings.

Methods: Pre-operative ¹⁸F-FDG PET/CT findings and parameters of maximum standard uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of primary lesion (MTV-P, TLG-P), and combination of primary lesion and metastases (MTV-C, TLG-C) were retrospectively analyzed in 24 patients with PSC confirmed by post-operative pathology. Tumor location, size, TNM stage, serum tumor markers, histopathological features, and mutations were also reviewed. Furthermore, progression-free survival (PFS) of 24 patients was analyzed.

Results: All 24 enrolled patients (20 men; 4 women; age: 62 ± 9 years) had single PSC, including 8 spindle cell carcinomas and 16 pleomorphic carcinomas. Serum levels of tumor markers were found to be abnormally increased sporadically. Six patients had central PSC, and 18 had peripheral PSC (diameter: 41 ± 16 mm). Eighteen lesions were located in the upper lobes of bilateral lungs, and 22 showed necrosis. Five cases were at TNM stage I, 12 at stage II, and 7 at stage III. The primary tumors were FDG avid in the 24 cases, with SUVmax of 17.2 ± 10.6. There were no correlations of SUVmax with tumor location, size, TNM stage, or histopathological subtypes. Programmed cell death ligand 1 (PD-L1) expression was detected in 21 cases (positivity rate: 87.5%). SUVmax of 17 lesions with PD-L1 expression degree ≥ 50% was obviously higher than that < 50% (P < 0.05). Kirsten rat sarcoma viral oncogene homolog (KRAS) gene mutation was found in six cases, and their SUVmax was significantly higher than that without KRAS mutation (P < 0.05). Furthermore, the median PFS of the 24 patients was 14 months, and 12-month and 24-month PFS rates were 55.9% and 27.8%, respectively. Only TLG-P and KRAS mutations of primary lesions were significantly associated with PFS.

Conclusions: PSC tended to present with intense ¹⁸F-FDG accumulation on PET/CT, and SUVmax was useful for assessing PD-L1 and KRAS expression of PSC. TLG-P and KRAS mutation were independent prognostic factors of PSC.