Pathological complete response (pCR) with or without the residual intraductal carcinoma component following preoperative treatment for pancreatic cancer: Revisiting the definition of “pCR” from the prognostic standpoint

BACKGROUND AND AIM: There are no previous reports describing the prognostic significance of the residual intraductal carcinoma component (carcinoma in situ [CIS]) following preoperative treatment for pancreatic ductal adenocarcinoma (PDAC). The aim of the present study was to investigate the prognostic significance of a minimal residual CIS in cases with complete absence of an invasive component after preoperative treatment for PDAC. METHODS: Eighty‐one of 594 PDAC patients with preoperative treatment and subsequent surgery in our institute showed remarkable remission in the invasive component, which included 48 patients with the minimal residual invasive component (Min‐inv group) and 33 with absence of an invasive component (No‐inv group). We assessed the survival of these patients in association with the presence or absence of an invasive component and intraductal CIS. RESULTS: Five‐year overall survival in the No‐inv group patients was significantly better than that of the Min‐inv group patients (82%/66%, P = .041). Among the 33 patients in the No‐inv group, residual CIS was observed in 16 patients (CIS‐positive group), and the remaining 17 patients had no residual CIS (CIS‐negative group). There was no significant difference in survival between patients in the CIS‐positive and CIS‐negative groups (92%/78%, P = .31). CONCLUSIONS: Residual CIS in the absence of an invasive component after preoperative treatment does not yield a prognostic impact after receiving perioperative treatment for PDAC. It might be reasonable to define pathological complete response (pCR) from the prognostic standpoint as follows: pCR is the complete absence of an invasive carcinoma component regardless of residual CIS.