BACKGROUND/OBJECTIVES: Depth of response (DpR
maximum % reduction from baseline in sum of the target lesion diameters) has demonstrated potential in predicting prognosis in several malignancies. However, its role in locally advanced pancreatic cancer (LAPC) is still unclear. In JCOG1407, modified FOLFIRINOX (mFOLFIRINOX) and gemcitabine plus nab-paclitaxel (GnP) exhibited comparable efficacy for LAPC. In this exploratory analysis using the data of JCOG1407, we focused on the association between DpR and prognosis. METHODS: DpR was classified into three groups at the tertile point and patients' backgrounds and survival were compared. The impact of DpR on survival outcomes was evaluated using the multivariable Cox proportional hazard model. RESULTS: Of the 126 patients enrolled in JCOG1407, 109 patients were included, categorized into three DpR groups: T1 (<
-37.2 %), T2 (-37.2 to -13.6 %), and T3 (>
-13.6 %). The median DpR was significantly greater in the GnP arm than in the mFOLFIRINOX arm (-28.9 vs. -22.7 %, P = 0.041). Median duration of response tended to be shorter in the GnP arm than in the mFOLFIRINOX arm, although the difference was not significant (5.3 vs. 8.2 months, P = 0.132). Greater DpR (T1) had a significantly larger impact on better progression-free survival (PFS) and overall survival (OS) than T3, with the hazard ratio of 0.469 (95 % confidence interval [CI] 0.268-0.821, P = 0.008), and 0.398 (95 % CI 0.217-0.728, P = 0.003), respectively. CONCLUSIONS: mFOLFIRINOX and GnP had similar OS, it is noteworthy that the regimens exhibited differences in DpR, with GnP leading to greater DpR. Greater DpR are associated with improved survival in patients with LAPC.