Abstract
Abstract
Objective:
To evaluate the diagnostic value of cytological greater omental milky spot examination for the diagnosis of peritoneal metastasis in gastric cancer patients.
Methods:
A total of 136 patients diagnosed with gastric cancer and without distant metastasis were enrolled in our study. All patients underwent laparoscopy and CH40 suspension liquid dye of peritoneal lymph nodes preoperatively as well as ascites or peritoneal lavage fluid collections and excisions of marked greater omental milky spot tissues perioperatively.
Results:
According to the laparoscopic results, the patients were divided into T1–T2 stage (n = 56) without and into T3–T4 stage (n = 80) with tumor invasion into the serosal layer. Among the T1–T2-stage patients, tumor cells could be detected in peritoneal lavage fluids in 2 cases, whereas with greater omental milky spot examination, peritoneal metastasis was detected in 8 cases. Among the 80 cases in the T3–T4 stage, tumor cells could be detected in 28 cases via peritoneal lavage cytology and in 43 cases by greater omental milky spot examinations, and 4 cases had cancer cell infiltration also in nonmilky spot omental areas. The statistical analysis showed that the staging accuracy rate of exfoliative cytology examination was superior to that of the laparoscopic exploration (P < .05), but its sensitivity was significantly lower than that obtained with cytological greater omental milky spot examinations (P < .05).
Conclusions:
The laparoscopic exploration could make a preliminary diagnosis of peritoneal metastasis via serosal layer invasion detection. For further analyses, cytological examinations of greater omental milky spots were more sensitive than exfoliative cytology.
Introduction
G
Computed tomography (CT) and magnetic resonance imaging are currently the most common methods in the preoperative staging of gastric cancer. 6 Also, positron emission tomography/CT has been recommended as superior post-therapy surveillance modality for the diagnosis of recurrent gastric cancer,7–9 but laparoscopic staging and peritoneal cytology have been considered to be the superior methods for gastric cancer staging and detecting preoperative metastases.10–13 However, since the significance of conventional peritoneal cytology results for predicting peritoneal recurrence is controversial,14–16 new approaches should be evaluated. Milky spots in the human greater omentum are accumulations of mononuclear cells comprising macrophages, B cells, T cells, and mast cells 17 and function as unique secondary lymphoid organs that promote immunity to peritoneal antigens. 18
In several animal studies it was shown that intraperitoneally injected cancer cells selectively aggregated in greater omental white spots19,20 and a medium conditioned by milky spot-containing adipose tissue caused 75% more cancer cell migration than did a medium conditioned by milky spot-deficient adipose. 21 Cao et al. suggested that omental milky spots are a highly efficient “natural filter” for screening gastric cancer stem cells. 22 Currently, the research on this topic is limited to animal models and no study on humans has been reported in the literature so far.
In our present study, we hypothesized that besides laparoscopic exploration and abdominal exfoliative cytology examinations, a greater omental milky spot pathological examination may be another option for the diagnosis of occult peritoneal metastasis and we compared the sensitivities of the above three methods for diagnosis of peritoneal metastasis in gastric cancer patients.
Patients and Methods
Patients
All patients were admitted to the general surgery department from June 2011 to June 2014. The inclusion criteria were as follows: (1) those who were diagnosed with gastric cancer confirmed by gastroscopy and pathological examinations before operation; (2) those who had no thoracic, abdominal, or posterior peritoneal metastasis excluded by thoracoabdominal CT examinations; and (3) those who were not treated with neoadjuvant chemo/radiotherapy. All laparoscopic interventions were performed by the same group of surgeons. The study was approved by the Ethics Committee of Haici Medical Group of Qingdao City and all participants signed informed consent.
Laparoscopic explorations
After successful anesthesia, the patients were brought into a supine position. Along with the inferior margin of the umbilicus, an incision with the length of 10 mm was made and CO2 was used to establish a pneumoperitoneum with a maintained intra-abdominal pressure of 12–14 mmHg. After puncture, a 10 mm cannula was placed for laparoscopic exploration. In case of obvious metastases in the abdominal visceral organs and peritoneum, the patients were sent to palliative surgery and excluded from the study. The remaining 136 patients included in this study were divided into T1–T2 stage (n = 56) without and into T3–T4 stage (n = 80) with tumor invasion into the gastric mucosa.
Dying of greater omental milky spots
The abdominocentesis was performed the day before operation. McBurney's point was selected as the puncture point with a deep venous needle. Then, a guide wire was implanted and along with the guide wire, a catheter was inserted through which CH40 suspension liquid (500 mL) was dripped into the abdominal cavity. Finally, the patients were told to change their positions.
Specimen collections
Peritoneal lavage cytology
After the abdomen was opened before the resections, ascites was extracted and in case no ascites was available, normal saline was used for lavage of the tumor and its surrounding tissues. After adding heparin, the detection liquids were centrifuged at 1500 rpm for 5 minutes, and the sediment smear was taken for further analysis. HE staining was performed after air drying, and the smear was observed under a microscope to seek cancer cells. The positive estimation criteria were as follows: (1) the sizes of cell nuclei were unequal; (2) the dye was deepened; (3) the nucleus was enlarged or irregular; and (4) there was visible mitosis or giant cancer cells.
Incision of the greater omental milky spot tissues
Before gastrectomy, 1 cm2 sized tissue samples from four of the CH40 marked milky spot areas and four 1 cm2 sized tissue samples from unmarked omentum tissue serving as control were excised. Then, pathological examinations were performed for the specimens of the two groups to observe micrometastasis cancer cells in the greater omental milky spot and nonmilky spot areas.
Statistical analysis
SPSS for Windows (Version 13.0.; SPSS, Inc., Chicago) was used for statistical analysis and Chi-square tests were applied for the statistical processing. P < .05 was regarded as statistically significant.
Results
A total of 136 patients with no distant metastasis were selected for our study, among which 88 were male and 48 were female, aged from 35 to 85 years with an average age of 68.5 ± 10.3 years. Among the 136 cases of gastric cancer, 56 cases had gastric serosa layer without change (T1–T2), and 80 cases had tumor invasion of gastric serosa layer (T3–T4). The basic characteristics of the patients are shown in Table 1.
Peritoneal metastasis detection
The peritoneal metastasis detection rates were significantly higher with the greater omentum pathological than with exfoliative cytology examination in T1–T2 patients ([8 (14.29%)] versus [2 (3.57%)]; (χ2 = 3.953, P < .05)) and T3–T4 patients ([43 (53.75%)] versus [28 (35.00%)]; (χ2 = 5.697, P < .05)), indicating that the greater omental milky spot detection was superior to the exfoliative cytology examination (Table 2).
Discussion
Laparoscopic exploration, an important means in diagnosis of peritoneal metastasis of gastric cancer with a higher diagnostic accuracy than that by the imaging examination, is of great significance in detecting the peritoneal metastasis and can also avoid the great damage derived from exploratory laparotomy.
Karanicolas et al. reported that the laparoscopic exploration was used to control the operation indications in 506 cases of gastric cancer patients, and the results suggested that futile laparotomy could be avoided in 30% of patients, which also might lead to reduced hospital mortality and shortened hospitalization time. 23 Also, Nakagawa et al. noted that in 22% of patients, unnecessary laparotomy could be avoided because of the staging laparoscopy. 11 In addition, staging laparoscopy had a significant impact on decisions regarding the treatment plan in patients with advanced gastric cancer and even for patients with aggressive treatment strategies. 24
The results of both metastatic cell detection methods revealed that the incidence was higher in T1–T2 stages compared to T3–T4 stages, indicating that the accuracy of laparoscopic explorations is associated with the tumor invasion of serosal layer. If the serosal layer is invaded, there is a higher probability of peritoneal metastasis, but for more sensitive detection, further analyses are necessary.
Peritoneal lavage as detection method for metastasis has been a matter of discussion. Bonenkamp et al. suggested that peritoneal lavage cytology increased the accuracy of staging and improved the selection of patients suitable for curative or palliative resection, 25 which has been supported also by other authors,11,26 whereas other studies reported that peritoneal lavage cytology is insensitive in predicting the development of peritoneal recurrence15,16,27 and Ki et al. noted the test execution variation that could be related to poor diagnostic accuracy and stage migration in patients with advanced gastric cancer. 28
Our cytological examination results revealed that the metastatic cell detection via pathological examination of greater omental milky spots was significantly more sensitive than with exfoliative cytology examination (8 versus 2, P < .05 for T1–T2 stages and 43 versus 28, P < .05 for T2–T4 stages).
It is known that macrophages in the milky spots secret C-C motif chemokine 22 (CCL22) thereby attracting C-C chemokine receptor type 4 (CCR4) expressing gastric cancer cells leading to their selective infiltration. Omental milky spots are a congenial microenvironment for peritoneal-free gastric cancer cells to migrate, survive, and establish cell cluster-type metastases.20,29 Since omental vessels express the angiogenic blood vessel-specific vascular endothelial growth factor receptor 3 (VEGFR3) and tumor cells colocalize with these vessels, the ability of tumors to induce neovascularization is probably increased. 30
In a systematic review of 28 related articles, intraperitoneal free cancer cells were associated with the risk of peritoneal recurrence and worse OS in gastric cancer patients, but the authors concluded that further incorporation of peritoneal cytology in clinical decision-making in gastric cancer depends on the development of a consistently accurate and rapid intraperitoneal free cancer cell detection method. 12
In our pilot study, we demonstrated that metastatic cell detection via pathological examination of greater omental milky spots after CH40 staining was significantly superior to exfoliative cytology for gastric cancer patients. Further analysis of correlations between recurrence as well as OS rates and greater omental milky spot cytological evaluations in gastric cancer patients is warranted.
In summary, the gastric tumor invasion into the serosal layer detected during laparoscopy was the first hint of peritoneal metastasis occurrence. The pathological examination of greater omental milky spots, which have been dyed with the CH40 before operation, led to a significant higher detection rate of peritoneal metastasis than exfoliative cytology in gastric cancer patients.
Footnotes
Disclosure Statement
No competing financial interests exist.