High Expression of DARPP-32 in Colorectal Cancer Is Associated With Liver Metastases and Predicts Survival for Dukes A and B Patients: Results of a Pilot Study

The purpose of this study was to investigate prognostic significance of Dopamine and cAMP-Regulated neuronal Phosphoprotein 32 (DARPP-32) expression in primary colorectal cancer. The study material consisted of clinical and histopathological data of 100 patients operated for colorectal cancer between 1994 and 1997. For immunohistochemical analysis, specific rabbit antibodies for DARPP-32 were used and the percentage of stained tumor cells was calculated under gross magnification (400 times) on a sample of 500 tumor cells. DARPP-32 expression in the primary tumor was significantly greater in patients with distant metastases compared to patients with no distant metastases (p=0.002). In multivariate regression analysis, DARPP-32 expression in the primary tumor was a significant predictor of distant metastases. With a cut-off point of 76.5%, DARPP-32 expression in the primary tumor significantly influenced both overall and disease free survival, especially for Dukes A and B patients (p=0.037). The results of this study indicate that DARPP-32 may be a potential marker of worse prognosis and a valuable tool for managing further adjuvant treatment in patients with stages Dukes A and B colorectal cancer.Key words: Colorectal neoplasms, Dopamine and cAMP-regulated phosphoprotein 32, Humans, Nerve tissue proteins, Liver metastasesColorectal cancer is the second most common cause of cancer related death in Western Europe and the United States, with the incidence of 50/100,000 population.¹ In spite of significant developments in surgery and new chemotherapy drugs and protocols as well as radiotherapy regimens, this malignancy still has high mortality.²The 5-year survival rate of colorectal cancer patients with Dukes A cancer ranges from 74 to 93%. Patients with Dukes B cancer have a 5-year survival of 40 to 82%, and those with positive lymph nodes (Dukes C) have a 5-year survival rate of 30 to 59%.^3,4 Recurrences are observed in as much as 34% of patients with Dukes A and B stage, compared with 59% in patients with lymph node metastases.⁵Liver metastases are a well proven major determinant of survival in patients with colorectal cancer.^2,6 Therefore, better selection of patients with potential to develop liver metastases or those having occult metastases may increase the survival of those patients in whom adjuvant therapies would not otherwise be indicated.^2,5,7Recently, overexpression of dopamine and 3′5′-cyclic adenosine monophosphate regulated neuronal phosphoprotein 32 (DARPP-32) has been found in several gastrointestinal adenocarcinomas.⁸ Although most of the research on this protein focused on its role in the central nervous system,^9–11 the finding of overexpression of this protein in cancer tissues brought up the hypothesis of its role in carcinogenesis.^8,12 Genetic studies led to the discovery of frequent 17q DNA amplifications in gastric cancer.⁸ Subsequently, the gene located at this site, called PPP1R1B, has been sequenced and found to encode DARPP-32 molecule, that was brought into connection with several malignancies.^8,13–18 The DARPP-32 molecule is a protein with molecular mass of 32 kDa, consisting of 204 amino acids and 4 phosphorylation sites: Thr34, Thr75, Ser102, and Ser137. Depending on the phosphorylation of 1 of these 4 amino acids, the DARPP-32 molecule is acting as the signal integrator and as the regulator of the phosphorylase and kinase activities in eukaryotic cells.¹⁹Basic research indicates that DARPP-32 may be associated with worse prognosis in some carcinomas.²⁰ However, it is remains unknown if evaluation of DARPP-32 expression in colorectal cancer patients may aid to evaluate prognosis.The purpose of this study was to investigate possible associations of DARPP-32 expression in primary colorectal cancer with known prognostic determinants of colorectal cancer and therefore set the basis for further clinical research.