The Impact of Molecular Subtyping on Pathological Staging of Pancreatic Cancer

Abstract

Background: The long-term outcomes following surgical resection for pancreatic ductal adenocarcinoma (PDAC) remains poor, with only 20% of patients surviving 5 years after pancreatectomy. Patient selection for surgery remains suboptimal largely due to the absence of consideration of aggressive tumor biology.

Objective: The aim of this study was to evaluate traditional staging criteria for PDAC in the setting of molecular subtypes.

Methods: Clinicopathological data were obtained for 5 independent cohorts of consecutive unselected patients, totaling n = 1298, including n = 442 that underwent molecular subtyping. The main outcome measure was disease-specific survival following surgical resection for PDAC stratified according to the American Joint Commission for Cancer (TNM) staging criteria, margin status, and molecular subtype.

Results: TNM staging criteria and margin status confers prognostic value only in tumors with classical pancreatic subtype. Patients with tumors that are of squamous subtype, have a poor outcome irrespective of favorable traditional pathological staging [hazard ratio (HR) 1.54, 95% confidence interval (CI) 1.04-2.28, P = 0.032]. Margin status has no impact on survival in the squamous subtype (16.0 vs 12.1 months, P = 0.374). There were no differences in molecular subtype or gene expression of tumors with positive resection margin status.

Conclusions: Aggressive tumor biology as measured by molecular subtype predicts poor outcome following pancreatectomy for PDAC and should be utilized to inform patient selection for surgery.

Figure 1

A, Transcriptomic profiling strategy of the molecular subtype cohort. Transcriptomic analysis was performed using either RNA sequencing (RNAseq) or gene expression microarray based on cellularity and adequate RNA quality of the sample in a selection (n = 442) of PDACs. Tumor cellularity >40% allowed whole genome sequencing, whilst RNAseq was performed in tumors with sufficient cellularity (>40%) and quality RNA. Kaplan-Meier survival curves for all patients stratified by AJCC 8^th edition staging criteria for B) T-stage, C) N-stage, and D) margin status and E) molecular subtype.

Figure 2

Kaplan-Meier survival curves for the APGI molecular subtype cohort using the AJCC 8^th staging criteria. Molecular subtypes were defined according to the Bailey classification as either squamous or classical pancreatic. T-stage is prognostic in (A) the entire cohort, or when stratified according to subtype as (B) classical pancreatic or (C) squamous. N-stage is prognostic in the (D) entire cohort and (E) the classical pancreatic subtype, but not (F) in the squamous subtype. Positive resection margin (R1 ≤1mm) is prognostic in (G) the entire cohort and (H) the classical pancreatic subtype, but not in (I) the squamous subtype.

Figure 3

Molecular differences between margin positive and negative PDAC. There was no significant difference between molecular subtype (A, B) or in gene expression using both RNAseq (C, E) or microarray analysis (D, F) between margin positive and margin negative PDAC. Significantly enriched genes are deemed up or downregulated at threshold of −2or +2. Log adjusted P value using Benjamini and Hochberg method. None of the up or downregulated genes reached this significance threshold.