Abstracts
1997 Digestive Disease Week

Correlation of apoptosis and p53, RB and BCL-2 expression with tumor stage and survival in colorectal cancer.

CA Ausch, GS Fan, GA Niehans, WD Wong, CJ Steer, RD Madoff. Division of Colon and Rectal Surgery, Department of Surgery, and Department of Medicine, University of Minnesota Medical School. Minneapolis, MN.

Spontaneous apoptosis contributes to retarding the growth of malignant tumors. Regulators of apoptosis include p53, RB, and BCL-2 and aberrations of their oncoproteins are implicated in colorectal carcinogenesis. PURPOSE: To assess the relationship of apoptosis and p53, RB, and BCL-2 expression on tumor stage and survival in colorectal cancer. METHODS: Archival tissue was obtained from 20 patients with Dukes B tumors, 20 patients with Dukes C tumors, and 10 patients with metastatic disease. Ten segments of normal colon were utilized as controls. Apoptotic cells were detected by end-labeling, and the apoptotic index was calculated as the percentage of apoptotic to total tumor cells. p53, RB, and BCL-2 expression was assessed by monoclonal antibody staining and was scored as follows: 0 <= 5%, 1: 5-25%, 2: 25-50%, 3: 50-75%, 4: >=75% of stained cells. All specimens were evaluated in a blinded fashion. Statistics were calculated utilizing the one-way ANOVA test. RESULTS: Shown in the following table:

                         Control     Dukes B      Dukes C     Dukes D
 Apoptotic cells (%)     5.1±5.6     3.5±3.0      1.1±1.0     0.5±0.6
 BCL-2                   1.1±1.0     1.3±0.8      2.0±0.7     2.6±1.1
 p53                     0.3±0.6     1.9±1.4      1.6±1.0     1.1±1.2
 RB                      1.0±1.0     2.5±0.8      2.5±1.0     2.5±0.6

The percentage of apoptotic cells decreased with advancing tumor stage. A statistically significant difference was found between stages C and D and control groups (p<0.01). Increased BCL-2 expression was observed in all tumor stages with a significant difference between stages B and C (p<0.05), stages B and D (p<0.001), stage C and control (p<0.05) and stage D and control (p<0.001). RB expression was increased in all tumor stages and was 2.5-fold higher in carcinomas than in controls with a significant difference between Dukes stages and controls (p<0.01). No correlation was determined for p53. Survival correlated significantly with apoptotic index (P < 0.01), but not with BCL-2, p53 or RB expression. CONCLUSIONS: Colorectal tumor stage is inversely correlated with the apoptotic index. Abnormally low levels of apoptosis are seen in tumors that have metastasized to lymph nodes and liver. BCL-2 expression, which inhibits apoptosis, has a positive correlation with tumor stage. In contrast, RB expression is increased equally in all stages compared to control. Because the effect of these markers on survival parallels that of the Dukes classification, these likely do not represent independent prognostic indicators.