The article by Dr. Kooby is an exellent review of the application of laparoscopy for gastrointestinal cancers, with particular reference to hepatic and pancreatic resections. It is especially appropriate, as we are currently noticing an increase in the need for minimally invasive oncologic surgery.

Immune Function, Malignancy, and Laparoscopy

The effects of pneumoperitoneum-based surgery can be broken down into two categories: (1) mechanical effects due to instrumentation and pressure of pneumoperitoneum, and (2) metabolic effects due to the chemical properties of the particular gas used (such as carbon dioxide). Establishing supraphysiologic concentrations of gas (carbon dioxide) that the body is actively trying to exhale can be associated with short-term and likely long-term metabolic consequences. Some of these include acidosis, alterations in cardiac function, and a differential effect on immune response. While the effects on acid-base balance and cardiorespiratory changes are usually self-limiting, it is not clear whether the effects on immune response have any bearing on the long-term oncologic outcome. In this regard, Dr. Kooby appropriately points out the differential effects of laparoscopy on systemic and local immune mechanisms.

The crucial role of natural killer cells and peritoneal macrophages in tumor immunity is highlighted by Dr. Kooby. It is well known that tumor-associated macrophages have been shown to display both pro- and antitumor activity and therefore are considered to play an important role in tumor immunity. In addition, some authors have also shown a correlation between macrophage counts and long-term outcome in malignancies involving the lung and breast. On the other hand, it has been also shown that CO₂ can significantly impair macrophage function. It remains to be seen if the CO₂ used during laparoscopic cancer surgery impairs the function of tumor-associated macrophages to the extent that it has any bearing on long-term oncologic outcome.

Port-Site Metastasis

The high incidence of port-site metastases reported initially in a small series of patients was alarming.[1] This was followed by a spate of animal experiments that had several drawbacks, as noted by Dr. Kooby, such as injecting cancer cells into nonorthotopic locations, using various routes of cancer cell delivery (cecal mesentry, intraperitoneal, portal vein, renal capsule, and transanal), having variable tumor cell volume, and using different endpoints for analysis. Finally, analyzing the effects of CO₂ pneumoperitoneum on tumors (located at sites distant from the abdomen) not directly exposed to CO₂ can be misleading. The author appropriately notes that these results are therefore to be interpreted with a measure of caution and may not exactly be extrapolated to the clinical situation. Subsequent reports in humans with large numbers of patients have noted an incidence of port-site metastases similar to that of open surgery in gynecologic malignancies (1,288 patients, 0.97%), gastrointestinal malignancies (435 patients, 0.5%), and genitourinary malignancies (10,912 patients, 0.09%).[2-4]

It is now clear that the incidence of port-site metastasis is equivalent to open surgery as long as sound oncologic principles are applied. Some additional precautions that are recommended in reducing the incidence of port-site metastasis include the following: Avoid excessive manipulation of the port sites, prevent dislodgement of the trocars, keep pneumoperitoneum at the lowest pressure possible to maintain visibility, use wound protectors when performing extracorporeal anastomoses, deflate the pneumoperitoneum with the trocars in place, and close the peritoneum when possible.

Hepatic and Pancreatic Resections

Laparoscopic liver and pancreatic resection requires expertise in both open liver/pancreatic surgery and advanced laparoscopic surgery, and therefore should be performed only in centers with a history of excellence in both. Liver resection has remained one of the last barriers in the use of laparoscopy due to several concerns, such as the inability to control bleeding in a rapid fashion, the difficulty of handling soft and friable tumors in the liver to assess margins, and the lack of proper instrumentation.

The risk of embolism through injured hepatic veins is present in both open and laparoscopic liver resection (LLR). This risk can be aggravated when using the argon beam coagulator during LLR due to the pressure of pneumoperitoneum and the inertness of argon gas. However, with improved instrumentation, several reports have shown that LLR is feasible and safe with short-term outcomes similar to or slightly better than open liver resection. Studies have documented that LLR can be performed with blood loss similar to or less than open liver resection. With the help of laparoscopic ultrasound, it has been noted that adequate margin width can be obtained with LLR. There have been no documented cases of CO₂ embolism in the recently published series of LLRs.[5]