Navigation

Characteristics Of Cancer Cells

Background: We sought a marker to differentiate malignant from nonmalignant pleural effusions. Methods: We studied 41 patients presenting with pleural effusions to the National Sanyo Hospital between April 2000 and January 2002 (33 men and 8 women; mean age, 68 years). Twenty patients (49%) were proven to have malignant pleural effusions, while 21 patients (51%) had nonmalignant pleural effusions. Thoracentesis was performed.

Results: The mean ([+ or -] SD) concentration of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) in malignant pleural effusions, measured by enzyme-linked immunosorbent assay, was significantly higher than that in nonmalignant pleural effusions (15.1 [+ or -] 33.6 vs 1.4 [+ or -] 0.81 U/mL, respectively; p < 0.05).

Conclusion: The determination of the RCAS1 concentration in pleural fluid is informative in the diagnosis of malignant pleural effusions.

Key words: diagnosis; lung cancer; pleural fluid

Abbreviations: RCAS1 = receptor-binding cancer antigen expressed on SiSo cells; SCC = squamous cell carcinoma

**********

Lung cancer, the most frequent cause of death from cancer also is a major cause of pleural effusion. Approximately 10% of lung cancer patients have a pleural effusion at the time of the initial diagnosis, and 30 to 40% develop pleural effusions later in their course. (1) Patients with malignant pleural effusion have a short life expectancy and are difficult to treat effectively. The management of lung cancer patients with pleural effusion requires effective treatment based on timely and accurate diagnosis.

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a type II membrane protein that is able to form oligomers through a coiled structure in its C-terminal portion. RCAS1 acts as a ligand for a putative receptor that is present in various human cell lines and on normal peripheral blood lymphocytes. (2) RCAS1 inhibits the growth of receptor-expressing cells in vitro and induces apoptotic cell death. (3) In previous immunohistochemical studies, RCAS1 was expressed in various malignant tissues, including lung cancer. (4,5) Soluble RCAS1 has been detected (6) by enzyme-linked immunosorbent assay in a culture supernatant derived from a human bile duct carcinoma cell line. These findings suggest that soluble RCAS1 may serve as a tumor marker. We investigated the concentrations of soluble RCASI in malignant and nonmalignant effusions to determine associations that may cause pleural effusions.

MATERIALS AND METHODS

Patients

Forty-one patients with pleural effusions who were admitted to the National Sanyo Hospital between April 2000 and January 2002 were studied. Clinical signs and symptoms, demographic data, and radiologic results were recorded. The clinical features of the patients are summarized in Table 1. The study group included 33 men and 8 women, with a mean age of 68 years. Malignant pleural effusions were present in 20 patients (49%), while nonmalignant pleural effusions were present in 21 patients (51%). Of these lung cancer patients, 12 had adenocarcinoma, 2 had squamous cell carcinoma (SCC), and 1 had small cell carcinoma.

Diagnosis of Malignant Pleural Effusions

Malignant pleural effusions were diagnosed either by pleural fluid cytologic findings or malignant cells identified in a pleural biopsy specimen. In addition, even when both of these test results were negative, malignant pleural effusion was diagnosed when a primary cancer was known to have disseminated and pleural fluid concentrations of established tumor markers were elevated. Fifteen of 20 cases were diagnosed by pleural fluid cytologic findings. Other cases were diagnosed by CT findings demonstrating multiple pulmonary or distant metastases. Carcinoembryonic antigen, SCC antigen, and cytokeratin 19 fragment in pleural fluid were elevated in three, one, and one cases, respectively.

Sample Collection and Determination of RACS1 Concentration

Each sample of pleural fluid was collected in a syringe during a thoracentesis performed after written informed consent was obtained. Samples were centrifuged at 2,000 revolutions per minute for I0 min, and the supernatant was frozen at -80[degrees]C until assayed. Soluble RACS1 concentrations were measured by sandwieh enzyme-linked immunosorbent assay using commercially available kits (Medical & Biological Laboratories; Nagoya, Japan).

Statistical Analysis

Differences in pleural fluid characteristics and RCAS1 between malignant and nonmalignant pleural effusions were examined by the Mann-Whitney test. Values of p < 0.05 indicated statistical significance.

RESULTS AND DISCUSSION

Differentiating between malignant and nonmalignant pleural effusions is a critical clinical problem, and conventional methods have proven to be inadequate. Cytologic examination of pleural fluid fails to detect neoplastic cells in 40 to 50% of malignant pleural effusions, and blindly performed pleural needle biopsy adds very little detection sensitivity. Several investigators1 therefore have sought to improve diagnosis by measuring tumor markers in pleural fluid. A reliable clinical marker providing a means of rapid and accurate diagnosis of malignant pleural effusion is greatly needed.

Many biological markers have been proposed to aid the diagnostic sensitivity in malignant pleural effusions, including carcinoembryonic antigen, cytokeratin 19 fragment 21-1, carbohydrate antigen 125, and SCC. Several previous reports demonstrated these markers to be significantly more abundant in malignant pleural effusions than in nonmalignant pleural effusions. In the present study, we focused on soluble RCAS1 in pleural fluid as a potential tumor marker.

As shown in Figure 1, the mean ([+ or -] SD) soluble RCASI concentrations in malignant pleural fluid were higher than those in nonmalignant pleural fluid (15.1 [+ or -] 7.8 vs 1.4 [+ or -] 0.18 U/mL, respectively; p < 0.05). Our results suggest that soluble RCAS1 should be an informative tumor marker for the diagnosis of malignant pleural effusion. No statistically significant correlation was observed between soluble RACS 1 and histologic type of lung cancer. In nonmalignant pleural fluid, there were no statistically significant correlations observed between tuberculosis and other infections.

Although the present study included only two eases of malignant mesothelioma, there was no statistically significant difference in soluble RACS1 concentrations in pleural fluid in malignant mesothelioma vs nonmalignant pleural fluid. Further studies should examine the utility of soluble RACS1 for the differential diagnosis between malignant mesothelioma and inflamed mesothelium.

In previous reports, (4.5) RCAS1 expression was significantly related to the overall survival of patients with various types of cancer. RCAS1 expression also has been reported to correlate with tumor progression and tumor invasiveness. Thus, the concentration of RCAS1 may indicate the aggressiveness of tumors behavior in humans. However, the role of soluble RCAS1 in the development of malignant pleural effusion is unknown, and further studies are required.

In conclusion, we describe for the first time that malignant pleura] fluid concentrations of soluble RCAS1 are significantly higher than those in nonmalignant pleural fluid. Despite its relatively high cost and lack of availability, the determination of the soluble RCAS1 concentration at the onset of pleural effusion may be diagnostically informative in patients with malignant pleural effusions in the clinical setting.

Table 1--Malignant vs Nonmalignant Pleural
Effusions *

Variables                          Total              Malignant

Patients, No.                       41                   20
Gender
  Male                              33                   14
  Female                             8                    6
Median age, yr                      72                   69
Range, yr                          29-88                44-80
Total protein, g/dL          4.4 [+ or -] 0.21     4.8 [+ or -] 0.23
LDH, IU/L                    947 [+ or -] 144     1014 [+ or -] 241
Glucose, mg/dL               120 [+ or -] 11       111 [+ or -] 13
Etiologies, No.
  Lung cancer                       15
  Pleural mesothelioma               2
  Breast cancer                      1
  Prostate cancer                    1
  Thyroid cancer                     1
  Tuberculosis                       9
  Infection other than TB            5
  Heart failure                      3
  Rheumatoid arthritis               1
  Nephrosis syndrome                 1
  Liver cirrhosis                    1
  Meigs syndrome                     1

Variables                      Nonmalignant

Patients, No.                       21
Gender
  Male                              19
  Female                             2
Median age, yr                      75
Range, yr                          29-88
Total protein, g/dL          4.0 [+ or -] 0.33
LDH, IU/L                    879 [+ or -] 165
Glucose, mg/dL               130 [+ or -] 19
Etiologies, No.
  Lung cancer
  Pleural mesothelioma
  Breast cancer
  Prostate cancer
  Thyroid cancer
  Tuberculosis
  Infection other than TB
  Heart failure
  Rheumatoid arthritis
  Nephrosis syndrome
  Liver cirrhosis
  Meigs syndrome

* Values given as mean [+ or -] SE, unless otherwise indicated.

LDH = lactate dehydrogenase; TB = tuberculosis.

ACKNOWLEDGMENTS: We wish to thank Drs. M. Moriyama, H. Kohara, K. Makihata, K. Takao, and K. Murakami for kindly providing clinical samples and offering critical comments.

* From the Departments of Respiratory Medicine (Drs. Aoe, Hiraki, Maeda, and Takeyama) and Clinical Research (Drs. Murakami and Sugi), National Sanyo Hospital, Respiratory Disease Center, Yamaguchi, Japan; and the First Department of Medicine (Dr. Yamazaki), Hokkaido University Graduate School of Medicine, Sapporo, Japan.

REFERENCES

(1) Reed CE. Management of the malignant pleural effusion. In: Paas HI, Mitchell JB, Johnson DH, et al, eds. Lung cancer: principles and practice. Philadelphia, PA: Lippincott-Raven, 1996; 643-654

(2) Nakashima T, Sonoda K, Watanahe T. Inhibition of cell growth and induction of apoptotic cell death by the human tumor associated antigen RCAS1. Nat Med 1999; 5:938 942

(3) Matsushima T, Nakashima M, Oshima K, et al. Receptor hinding cancer antigen expressed on SiSo cells, a novel regulator of apoptosis of erythroid progenitor cells. Blood 2001; 96:313-321

(4) Kaku T, Sonoda K, Kamura T, et al. The prognostic significance of tumor-associated antigen 22-1-1 expression in adenocarcinoma of the uterine cervix. Clin Cancer Res 1999; 5:1449-1453

(5) Izumi M, Nakanishi Y. Yoshino I, et al. Expression of tumor-associated antigen RCAS1 correlates significantly with poor prognosis in nonsmall cell lung carcinoma. Cancer 2001; 92:446-451

(6) Enjoji M, Nakashima M, Nishi H, et al. The tumor-associated antigen, RCASI, can be expressed in immune-mediated disease as well as in carcinomas of biliary tract. J Hepatol 2002; 36:786-792

Manuscript received November 3, 2003; revision accepted May 6, 2004.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (e-mail: permissions@chestnet.org).

Correspondence to: Keisuke Aoe, MD, PhD, Department of Respiratory Medicine and Clinical Research, National Sanyo Hospital, Respiratory Disease Center; 685 Higashi-kiwa, Ube, Yamaguchi 755-0241, Japan; e-mail: keisukeaoe@mtf.biglobe.ne.jp

COPYRIGHT 2004 American College of Chest Physicians
COPYRIGHT 2004 Gale Group