Peritoneal Involvement Shortened Survival in Metastatic CRC

Patients with peritoneal metastatic colorectal cancer had significantly shorter overall survival compared with patients with other isolated sites of metastases, according to the results of a study published in Lancet Oncology.

“Peritoneal metastases are associated with worsened prognosis whether isolated or in combination with other metastatic locations, and when in combination with other locations, overall survival worsens with increasing number of metastatic sites,” wrote Jan Franko, MD, of the division of surgical oncology at Mercy Medical Center in Des Moines, Iowa, and colleagues.

The researchers looked at data from 10,553 patients taken from 14 phase III randomized trials performed between 1997 and 2008. The majority of patients included (87%) had non-peritoneal metastatic colorectal cancer; 2% of patients had isolated peritoneal metastatic colorectal cancer and 11% of patients had peritoneal disease with other organ involvement.

The data revealed several trends among patients with peritoneal colorectal cancer compared with non-peritoneal involvement. These patients were more likely to be women (41% vs 36%; P = .0003), have primary colon tumors (84% vs 66%; P < .0001), and have an Eastern Cooperative Oncology Group (ECOG) performance status of 2 (10% vs 6%; P < .0001). In addition, there was a higher proportion of patients with mutated BRAF among patients with peritoneal-only (18%) and peritoneal metastatic colorectal cancer with other sites of involvement (12%) compared with non-peritoneal disease (9%; P = .028). The number of patients with KRAS mutations was equally distributed between the groups.

Patients with non-peritoneal disease had significantly better overall survival (adjusted hazard ratio [HR], 0.75 [95% CI, 0.63–0.91]; P = .003). Patients with isolated peritoneal metastases and those with peritoneal metastases with two or more additional sites had the shortest overall survival of any group (HR, 1.40 [95% CI, 1.14–1.71]; P = .0011). Overall survival for patients with two or more non-peritoneal metastatic sites (HR, 1.04) and peritoneal metastatic disease plus one other site (HR, 1.10) had similar survival to those with isolated peritoneal metastases.

It is possible “that poorer survival in patients with metastatic colorectal cancer with multiple disease sites is a function of both increased number of metastatic sites and peritoneal involvement,” according to the researchers. “This finding suggests prognostic heterogeneities exist in this group.”

Franko and colleagues acknowledged that the conclusions from this study are different than those of the only prior study looking at peritoneum-only metastatic involvement.

“While we noted that patient prognosis with peritoneal-only metastases was similar to those with two non-peritoneal disease sites (both M1b stage), the other report suggested that peritoneal-only involvement carries prognosis similar to patients with metastasis at a single site and better prognosis as compared with patients with metastasis in multiple organs,” the researchers wrote. “A larger patient sample and better data collection in context of randomized trials are probably the main reasons for enhanced discrimination in our study.”