External referrals for cytoreductive surgery yield significant insights for surgeons.

• Out-of-system (OOS) patients had a higher peritoneal carcinomatosis index (PCI) of 18.5 versus 13.0 for in-system (IS) patients.
• OOS patients required longer operative times (518 minutes vs. 321 minutes) and had longer hospital stays (14 days vs. 9 days).
• Despite higher burdens, OOS patients achieved similar completeness of cytoreduction (85% OOS vs. 87.7% IS).

Surgeons should consider referral pathways, as many OOS patients previously deemed unresectable achieved complete cytoreduction at high-volume centers.