Bidirectional Chemotherapy in Peritoneal-Limited Metastatic Gastric Cancer: A Case Study of Complete Pathological Response

Introduction
Peritoneal metastasis in gastric cancer presents a challenging clinical scenario with limited treatment options and poor prognosis. Bidirectional chemotherapy, combining systemic and intraperitoneal agents, has emerged as a possible promising strategy. However, evidence supporting its efficacy in achieving curative outcomes remain scarce.

Case Presentation
We report a case of a 74-year-old Chinese male who presented with stage 4 gastric adenocarcinoma. He presented with dyspepsia and esophago-gastroduodenoscopy showed a fungating antral tumour. Histology revealed a moderately differentiated adenocarcinoma. While staging CT scan did not show evidence of metastatic disease, diagnostic laparoscopy yielded peritoneal washings suspicious for metastatic adenocarcinoma.
He was offered bidirectional chemotherapy given good functional status and peritoneum-limited disease with view of possible conversion surgery as an alternative to standard of care palliative chemotherapy and was keen.

He was treated with bidirectional chemotherapy comprising of Xelox and Trastuzumab regimen alongside intraperitoneal paclitaxel. Diagnostic laparoscopy was repeated after 4 cycles, which showed a 2cm calcified nodule over the falciform, suspicious for peritoneal deposit – consistent with PCI score of 2. While peritoneal washings were negative, histology of the nodule showed post treatment changes. Subsequently, he underwent another 4 cycles of chemotherapy, and showed remarkable response with resolution of peritoneal disease confirmed with repeat diagnostic laparoscopy and radiological imaging.

He underwent laparoscopic subtotal gastrectomy with D2 lymphadenonectomy, Roux-En-Y reconstruction with hyperthermic intraperitoneal chemotherapy (HIPEC). Intraoperatively, no obvious disease was seen and no gross serosal disease was noted in stomach specimen. Final histology showed no residual adenocarcinoma, indicative of complete pathological response to treatment. Peritoneal washings were also negative for malignancy.

Conclusion
This case highlights the potential of bidirectional chemotherapy as a neoadjuvant approach for peritoneal-limited metastatic gastric cancer, leading to complete pathological response and allowing for curative surgery. Further studies are warranted to validate the efficacy and safety of this treatment option.