Effect of oxaliplatin‐based chemotherapy on chemosensitivity in patients with peritoneal metastasis from colorectal cancer treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy: proof‐of‐concept study

BACKGROUND: Chemosensitivity testing, including collagen gel droplet‐embedded culture drug sensitivity test, has proven to be a useful tool in therapeutic decision‐making. This retrospective analysis investigated chemosensitivity testing of peritoneal metastases collected during cytoreductive surgery (CRS), and its impact on survival in patients with colorectal cancer. METHODS: All patients with peritoneal metastasis from colorectal cancer who underwent CRS with or without hyperthermic intraperitoneal chemotherapy (HIPEC) between November 2008 and October 2014 were included. The growth inhibition rate was expressed as the ratio between the image density after treatment (T) and that before treatment (control, C). Tumours with a reduction in T/C ratio of less than 20 per cent were defined as resistant and those with a reduction of 20 per cent or more as sensitive. Groups were compared for overall (OS) and disease‐free (DFS) survival. RESULTS: Of 84 eligible patients, 81 received neoadjuvant chemotherapy (NACT), including 56 patients with an oxaliplatin‐based regimen. Mean(s.d.) follow‐up was 23·4(22·9) months. The median overall survival of all patients was 19·0 (i.q.r. 5·7–36·1) months, with a progression‐free survival time of 10·1 (4·5–17·0) months. Patients who received oxaliplatin‐based NACT had significantly altered chemosensitivity to oxaliplatin; only 20 of 51 such patients showed chemosensitivity to oxaliplatin compared with 16 of 24 who did not undergo oxaliplatin‐based NACT (P = 0·046). However, patients who showed chemoresistance to oxaliplatin had similar OS to those with chemosensitivity (18·8 versus 18·1 months; P = 0·835). The choice of HIPEC agents in patients who received oxaliplatin‐based NACT did not significantly influence survival (oxaliplatin versus mitomycin C: median OS 20·6 (10·9–24·8) versus 19·0 (10·5–34·6) months, P = 0·811; DFS 6·6 (2·8–25·7) versus 9·3 (4·1–13·9) months, P = 0·191). CONCLUSION: Patients who had oxaliplatin‐based NACT showed a higher rate of chemoresistance to oxaliplatin at the time of CRS and HIPEC. The impact of chemosensitivity testing on OS remains unclear and needs further investigation.