Retrospective Evaluation of the Prognostic Value of Histological Growth Pattern in Patients with Colorectal Peritoneal Metastases Undergoing Curative-Intent Cytoreductive Surgery

Background Two distinct histological growth patterns (HGPs) were described in patients with peritoneal metastasis of colorectal cancer origin (PMCRC) with limited Peritoneal Cancer Index (PCI) <= 6 who did not receive neoadjuvant chemotherapy (NAC) and were treated with cytoreductive surgery (CRS) hyperthermic intraperitoneal chemotherapy (HIPEC): pushing HGP (P-HGP) and infiltrating HGP (I-HGP). Patients with dominant P-HGP (>50%) had significantly better disease-free survival (DFS) and overall survival (OS). Objective We aimed to determine whether these previous observations regarding the prognostic value of HGP in patients with PMCRC with low PCI (<= 6) are also valid in all operable patients, regardless of whether they received NAC or not and regardless of PCI score. Methods This was a retrospective study including 76 patients who underwent complete CRS HIPEC for PMCRC between July 2012 and March 2019. In each patient, up to five of the largest excised peritoneal nodules were analyzed for their tumor-to-peritoneum interface. Correlations between NAC, HGP, and prognosis were further explored. Results Thirty-seven patients (49%) had dominant P-HGP and 39 (51%) had dominant I-HGP. On univariate analysis, patients with P-HGP <= 50% had significantly lower OS than those with dominant P-HGP >50% (39 versus 60 months; p=0.014) confirmed on multivariate analysis (hazard ratio 2.4, 95% confidence interval 1.3-4.5; p=0.006). There were no significant associations between NAC and type of HGP. Conclusions This study confirms the prognostic value and reproducibility of the two previously reported HGPs in PMCRC. Dominant P-HGP is associated with better DFS and OS in patients undergoing curative-intent CRS +/- HIPEC compared with I-HGP, independently of the extent of peritoneal disease burden.