Colorectal cancer cells from patients treated with FOLFOX or CAPOX are resistant to oxaliplatin.

Numerous studies have suggested benefit for heated intraperitoneal chemotherapy (HIPEC) in the treatment of peritoneal metastases from colon cancer. However, the PRODIGE 7 trial that randomized 265 colon cancer patients to surgery plus HIPEC vs. surgery alone after neoadjuvant chemotherapy (NACT) did not confirm benefit. These data were published as an abstract and not as a peer-reviewed manuscript. One concern is that prior drug exposure may select for drug resistance and blunt HIPEC efficacy. A database query identified colon cancer specimens evaluated for chemotherapy sensitivity by ex-vivo analysis of programmed cell death (EVA/PCD), a primary culture platform that examines drug-induced cell death (apoptotic & non-apoptotic) by morphologic, metabolic and histologic endpoints. Of 87 fresh colon cancer specimens, 54 (62%) were untreated and 33 (38%) had received prior folinic acid, 5-fluorouracil, oxaliplatin (FOLFOX) or capecitabine and oxaliplatin (CAPOX). In an apoptosis assay, the lethal concentration of 50% (LC50) in untreated patients was significantly lower than in patients treated by FOLFOX (p = 0.002). Then to approximate PRODIGE 7, treated patients were separated by having received oxaliplatin treatment less than or greater than 2 months before EVA/PCD analysis. The degree of resistance increasing significantly for patients who received treatment less than 2 months prior to EVA/PCD (p < 0.002). Activity for mitomycin and irinotecan was not significantly different for untreated vs. treated patients, but 5-FU was more resistant (P = 0.048). The failure of PRODIGE 7 to improve survival with surgery plus HIPEC following NACT may reflect diminished oxaliplatin cytotoxicity in patients whose residual disease has been selected for oxaliplatin and 5-FU resistance. [ABSTRACT FROM AUTHOR]