BACKGROUND: Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) enable effective management of colorectal and appendiceal peritoneal metastases (CAPM) despite high morbidity. This study aimed to evaluate the role of repeat diagnostic laparoscopy (rDL) after systemic ± intraperitoneal chemotherapy in the management of initially unresectable CAPM. METHODS: This retrospective cohort study included 70 consecutive patients with CAPM who underwent initial diagnostic laparoscopy (iDL). Patients with inoperable or equivocal CAPM underwent chemotherapy followed by rDL to assess the treatment response and possibility of conversion to CRS and HIPEC. RESULTS: Cytoreductive surgery was deemed feasible for 29 patients and unlikely or equivocal for 41 patients based on iDL. Of the 29 resectable patients, 24 successfully underwent CRS and HIPEC after neoadjuvant chemotherapy. Among the 41 patients initially considered unresectable, 16 were deemed operable based on rDL after chemotherapy, and CRS and HIPEC were achieved for 14 patients (conversion). The median peritoneal cancer index was significantly reduced after chemotherapy for the 14 "conversion" patients, from 16 based on iDL to 11 based on rDL (p <
0.05). The conversion rate was 34% (14/41), with a 5-year survival rate of 14%. Treatment with CRS and HIPEC was achieved for 38 of 45 patients deemed operable based on either iDL or rDL (worst-case estimated positive predictive value, 84%). CONCLUSION: Diagnostic laparoscopy is useful in predicting the likelihood of achieving CRS for patients with CAPM. Despite inoperability based on iDL, patients should be considered for rDL after chemotherapy to assess the possibility of conversion to CRS and HIPEC.