Depth of Liver Invasion as a Novel Predictor for Outcome of Perihilar Cholangiocarcinoma.

The current American Joint Committee on Cancer (AJCC) pT classification was inaccurate in predicting prognosis for perihilar cholangiocarcinoma (pCCA). This study aimed to propose a novel classification based on the depth of liver invasion (DOLI) of pCCA. Patients who underwent major hepatectomy combined with caudate lobectomy for pCCA between January 2015 and June 2023 were reviewed retrospectively. The maximum straight-line distance from the hepatic hilar plate to the infiltrated liver parenchyma was measured as DOLI. Log-rank statistics were used to determine the cutoff points. Among 167 patients, liver invasion was observed in 100 patients (59.9%). The cutoff points of DOLI for prognosis were 0 mm and 2.5 mm. DOLI was stratified into grade 1 (DOLI=0 mm; 67/167, 40.1%), grade 2 (0 mm<DOLI ≤ 2.5 mm; 63/167, 37.7%), and grade 3 (DOLI >2.5 mm; 37/167, 22.2%). The DOLI grade was associated with CA19-9 levels, tumor size, lymph node metastasis, perineural invasion, and portal vein invasion. The DOLI grade was an independent prognostic factor for both overall survival (OS) and recurrence-free survival (RFS) (both P <0.001), and demonstrated superior prognostic discrimination compared with the pT classification (C-indexes for OS and RFS: 0.67 vs. 0.63; 0.64 vs. 0.61). In conclusion, DOLI was an accurate prognostic indicator for pCCA. The 3-tier DOLI grades with cutoff points of 0 and 2.5 mm may serve as a potential alternative to the current pT classification.