Background
The development of new perioperative treatment modalities to activate the immune system in colorectal cancer might have a beneficial effect on reducing the risk of recurrence after surgery. Calcium electroporation is a promising treatment modality that potentially modulates the tumor microenvironment. The aim of this study was to evaluate the safety of the procedure in the neoadjuvant setting in localized left-sided colorectal cancer (CRC).

Methods
The study included patients with potentially curable sigmoid or rectal cancer with no indication for other neoadjuvant treatment. Patients were offered calcium electroporation as a neoadjuvant treatment before elective surgery. Follow-up visits were conducted on the preoperative day before elective surgery, POD2, POD14, and POD30, with an evaluation of adverse events, impact on elective surgery, clinical examination, and quality of recovery.

Results
Endoscopic calcium electroporation was performed as an outpatient procedure in all 21 cases, with no procedure-related complications reported. At follow-up, five adverse events were registered, two of which were classified as serious adverse events. Surgery was performed as planned in 19 patients (median time to surgery, 8 days), and the final two patients underwent surgery with a delay due to adverse events (14 and 33 days). No significant impact on the quality of recovery scores nor inflammatory markers were seen before and after calcium electroporation, nor baseline and POD30.

Conclusions
Endoscopic calcium electroporation is a safe and feasible procedure in patients with potentially curable CRC. The study showed limited side effects and limited impact on the following elective surgical resection.