Key messages

• Due to a lack of robust evidence, the benefits and risks of adding chemotherapy directly into the abdominal cavity (intraperitoneal chemotherapy, or IPC) for stomach cancer are unclear.

• IPC combined with surgery may help people with stomach cancer live longer, both in those at high risk of cancer spread and in those with confirmed spread to the abdomen. IPC may have little to no effect on specific complications like leakage where the stomach is reconnected after surgery (anastomotic leakage). However, we are very uncertain about these results, and safety and well-being outcomes are poorly reported.

• More high-quality research, especially from non-Asian countries, is needed to better understand IPC effectiveness and safety.

What is gastric cancer with peritoneal metastasis, and how can it be treated?

Stomach cancer (gastric cancer) is one of the most common cancers worldwide. When found early and confined to the stomach, such early-stage cancer is treated with surgery to remove the tumor completely (radical surgery).

Sometimes, stomach cancer spreads to the abdominal cavity, leading to a condition called peritoneal metastasis. This is difficult to treat, and surgery cannot remove all cancer. Treatment relies mainly on chemotherapy. In selected cases, surgery to reduce tumor burden (cytoreductive surgery) may be used.

Standard chemotherapy given through veins (systemic chemotherapy) does not reach the abdominal cavity effectively. To improve treatment, doctors have explored giving chemotherapy directly into the abdominal cavity (intraperitoneal chemotherapy or IPC). Early studies replaced standard chemotherapy with IPC; recent studies added IPC to usual care. However, it is still unclear whether IPC is helpful or harmful. More evidence is needed to guide treatment decisions.

What did we want to find out?

We wanted to find out whether IPC can help people with stomach cancer by:

• improving survival;

• slowing cancer worsening, such as recurrence or progression; and

• improving well-being.

We also needed to check whether there are any problems with giving IPC to people with stomach cancer, such as:

• causing harmful effects, including those that are serious;

• causing complications such as leakage where the stomach is reconnected after surgery (anastomotic leakage), or serious abdominal infection (abdominal abscess).

We looked at two different uses of IPC in the context of systemic chemotherapy, based on the stage of cancer and the type of surgery.

• Prophylactic IPC: IPC given with radical surgery for people at high risk of peritoneal metastasis.

• Therapeutic IPC: IPC given with cytoreductive surgery for people with confirmed peritoneal metastasis.

What did we do?

We searched for studies comparing IPC with no IPC in people having stomach cancer surgery. We summarized the results and assessed how confident we could be in the findings, based on study design, size, and reporting quality.

What did we find?

We found nine studies involving 829 people, mostly from China. Seven studies (656 people) assessed prophylactic IPC, and two studies (173 people) assessed therapeutic IPC. Follow-up ranged from 0.2 months to 83.5 months. Five studies received funding.

We are very uncertain about all results due to limited evidence.

• Prophylactic IPC compared to no IPC

  • IPC may help people live longer (6 studies, 522 people).

  • IPC may make little or no difference in preventing cancer recurrence (1 study, 134 people).

  • IPC may make little or no difference to anastomotic leakage (4 studies, 366 people) or abdominal abscess (1 study, 105 people).

  • No studies reported serious harmful effects, well-being, or total side effects.

• Therapeutic IPC compared to no IPC

  • IPC may help people live longer (2 studies, 173 people).

  • IPC may make little or no difference to the risk of serious harmful effects or anastomotic leakage (1 study, 68 people).

  • One study suggests IPC may delay cancer progression (1 study, 105 people).

  • IPC may make little or no difference to well-being (1 study, unclear number of people).

  • No studies reported abdominal infections or total side effects.

What are the limitations of the evidence?

Our confidence is limited because many studies had flaws, small sample sizes, and few events reported. In addition, most studies did not report on our main outcomes of interest. These results are unlikely to reflect the results of all the studies that have been conducted in this area, some of which have not made their results public yet.

How up to date is this evidence?

This evidence is current to 12 June 2025.