Neoadjuvant Treatment of Resectable or Locally Advanced Borderline Pancreatic Adenocarcinoma: Reproducibility of Tumor Measurement in CT Versus MRI

Despite important therapeutic advances, pancreatic adenocarcinoma remains one of the cancers with a high mortality rate (4th leading cause of cancer death in the US in 2021), poor prognosis (5-year overall survival rate of 10%) and increasing incidence.

Patients are often metastatic from the start or at an advanced stage at diagnosis, making curative treatment difficult to envisage. Although the gold standard of treatment for resecable pancreatic adenocarcinoma is initial surgery followed by adjuvant chemotherapy, considerable interest has emerged in a treatment strategy involving neoadjuvant therapy in patients at high risk for positive resection margins (R1) on initial imaging workup.

The assessment of response to neoadjuvant therapy is complex, especially for the evaluation of vascular invasion with a high risk of overestimating residual invasion after neoadjuvant therapy. Accurate assessment of tumor size before and after neoadjuvant treatment is therefore crucial to identify good responders (according to RECIST 1.1 criteria) and thus improve the selection of patients who can benefit from curative surgery with healthy resection margins (R0).

In clinical practice, tumor size assessment is performed by injected computed tomography (CT). The latter has certain advantages in terms of technical reproducibility, but has a number of limitations. Indeed, the delineation of the tumor mass in CT seems to be subject to a significant inter-observer variability. The same is true for vascular invasion. CT also seems to underestimate the size of the tumor compared to the anatomopathological examination of the surgical specimen. On the other hand, Magnetic Resonance Imaging (MRI) has been shown to be superior to CT in tumor detectability and diagnosis of malignancy in the presence of an indeterminate pancreatic mass. It has also been shown that tumor size, whether measured in diameter or volume, is frequently underestimated on CT compared to multiparametric MRI or pathological examination of the resection specimen.

In the latest recommendations of the National Comprehensive Cancer Network (NCCN), MRI is indicated at diagnosis in non-metastatic patients with indeterminate liver lesions on CT, or as a second-line alternative to CT for re-evaluation after neo-adjuvant therapy in patients with resectable or borderline resectable disease according to the NCCN classification. However, MRI is increasingly performed routinely in some centers, both at diagnosis and at re-evaluation after neo-adjuvant therapy. The question of which imaging modality between CT and multiparametric MRI is the most reproducible in terms of tumor size measurement becomes important, especially in the evaluation of the response to neoadjuvant therapy. A few studies have investigated the interobserver variability of tumor size measurement in CT versus MRI in the context of radiotherapy management for the delineation of an irradiation field, but to date investigators have not found any study evaluating the interobserver variability of tumor size measurement using RECIST criteria before and after neoadjuvant treatment for pancreatic adenocarcinoma.