Histological tumor response predicts clinical outcome in patients with colorectal peritoneal metastasis treated with preoperative chemotherapy followed by cytoreduction and HIPEC.

Objectives: Up to one quarter of the patients with colorectal cancer (CRC) develop peritoneal carcinomatosis (PM). The aims of this retrospective study were to characterize the histological response of the PM of CRC to preoperative chemotherapy and evaluate the potential prognostic value, in terms of survival.

Methods: This retrospective unicentric study evaluated a group of 30 patients treated between 2010 and 2020 at the São João University Hospital Center with preoperative chemotherapy, followed by cytoreduction surgery plus hyperthermic intraperitoneal chemotherapy. The evaluation of the histological response was done using two scores: the tumor regression grading (TRG) and the peritoneal regression grading score (PRGS).

Results: Mean post-procedure survival is higher in the PRGS 1-2 group (74.19 months) vs. the PRGS 3-4 group (25.27 months) (p=0.045), as well as in the TRG 1-2 group (74.58 months) vs. TRG 4-5 (25.27 months) (p=0.032). As for progression-free survival (PFS), the PRGS 1-2 group had a mean value of 58.03 months vs. PRGS 3-4 which had 11.67 months (p=0.002). Similar was observed with the TRG 1-2 group, which had a mean PFS of 61.68 months vs. TRG 4-5 with 11.67 months (p=0.003).

Conclusions: A better histological response to preoperative chemotherapy, represented as a lower PRGS and TRG value, is associated with longer post-procedure survival and progression-free survival in this group of patients. That is, these two scores have prognostic value.