The prognostic impact of oligometastases in patients treated with cytoreductive surgery and HIPEC – a Swedish population-based study

Abstract Introduction In selected patients, colorectal peritoneal metastases (PM) with synchronous oligometastatic disease, defined as limited liver, lung, or non-regional lymph node metastases, can be treated with cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). This study aimed to evaluate the prognostic impact of oligometastases. Method Data were extracted from the Swedish HIPEC registry for all patients with colorectal PM treated with CRS and HIPEC between 2013 and 2023 in Sweden. Result Among the 632 patients who underwent complete CRS and HIPEC, 112 (18%) had oligometastases. Open-close laparotomies were similar between the groups. Within the oligometastatic cohort, 54 (48%) had liver, 5 (5%) lung, and 36 (32%) lymph node metastases as the only site. Seventeen patients (15%) had metastasis at two sites. Median peritoneal cancer index was 9 in both groups. Neoadjuvant treatment was more common in the oligometastatic group (38% vs. 19%, p<0.001), whereas signet ring cells were more frequent in the non-oligometastatic group (12 % vs. 6%, p=0.03). Five-year overall survival (OS) was 38% (95% CI:32–45) in the non-oligometastatic group and 25% (95% CI:15–43) in the oligometastatic group (p=0.3). Among patients with isolated liver metastases, survival was 19% (95% CI:8–44), and 29% (95% CI:12–72) in those with isolated lymph metastases. Recurrence-free survival was 5% (95% CI: 2–14) in the oligometastatic group, compared to 12% (95% CI: 9–16, p=0.01). Discussion Oligometastatic disease was not associated with a significant difference in OS. However, recurrence-free survival was markedly poor, with most patients experiencing recurrence. Nevertheless, oligometastatic disease should not exclude appropriately selected patients from CRS and HIPEC.