Purpose: The deleted in colorectal cancer (DCC) gene predicts a poor outcome for patients with colorectal carcinoma. This study was designed to investigate whether the expression of the DCC protein also can predict response to adjuvant chemotherapy.
Methods: The expression of DCC was evaluated immunohistochemically in 74 paraffin-embedded tumor samples from patients with Stage II (n = 41) and Stage III (n = 33) colorectal carcinomas. Follow-up time was at least 60 (median, 64) months. Follow-up was at least five years for all patients who are alive. End points of the study were recurrence of disease and death. Forty-eight patients received adjuvant therapy of 5-fluorouracil + levamisole; 28 were not treated.
Results: Fifty percent of tumors were deleted in colorectal cancer-positive (DCC+). Proportion of survival and disease-free survival were higher in the DCC+ patients (83 percent) than in deleted in colorectal cancer-negative (DCC-; 54 percent). In the DCC+ group, adjuvant treatment was a strong positive predictive factor for survival and disease-free survival. All DCC+ patients who received adjuvant chemotherapy (CHEMO+) are alive with no evidence of disease, whereas without chemotherapy (CHEMO-) only 54 percent are alive ( P = 0.0001). When stratification was performed by stage, patients in Stage II who were DCC+/CHEMO+ had survival and disease-free survival of 100 percent, whereas in DCC+/CHEMO- survival rate was 75 percent and disease-free survival rate 62 percent ( P = 0.042). Patients in Stage III who were DCC+/ CHEMO+ had survival and disease-free survival of 100 percent, whereas in DCC+/CHEMO- both dropped to zero ( P = 0.0002). On the other hand, in the DCC- tumors, there was no statistical significant relationship between chemotherapy and survival or disease-free survival (DCC-/CHEMO- had 57 percent survival; DCC-/CHEMO+ had 52 percent survival).
Conclusions: DCC is a prognostic factor for colorectal cancer. Positive expression of DCC identifies a subgroup of patients who respond favorably to adjuvant chemotherapy, which resulted in our cases, in 100 percent survival and disease-free survival rates. Without treatment, the survival rate of DCC+ patients dropped significantly. We suggest that DCC immunostaining should be performed routinely. All DCC+ patients should receive adjuvant chemotherapy. For DCC- tumors, a larger cohort of patients should be studied before definitive conclusions can be drawn; however, clinical trials of new drug combinations should focus on DCC- patients.