The expression of proliferating cell nuclear antigen (PCNA) and Ki-67 in patients with colorectal adenocarcinoma and lymph node metastases

Background: In patients with colorectal cancer (CRC), the presence of lymph node (LN) metastases involvement seriously reduces recovery rate and survival. Unfortunately, despite a careful lymphadenectomy and subsequent histopathological assessment of resected LNs, up to 15-20% of N0 patients who underwent curative (R0) resection develop tumor recurrence. With the aim of reducing false-negative results, various more sensitive methods for tumor cell detection based on immunohistochemical techniques or reverse transcriptase polymerase chain reaction (RT-PCR) detection of mRNA, have been suggested. However, the aggressiveness of CRC and the subsequent likelihood of LNs or distant metastases mainly depends on proliferative activity of cancer cells within cancer tissue revealed by several measurable molecular markers, including proliferating cell nuclear antigen (PCNA) (a non-histamine nuclear protein), p53, COX-2, EGFR, HER2, and Ki-67 (a marker of mitotic activity) expression. The aim of this study was to evaluate the predictive value of Ki-67 overexpression and PCNA positivity in predicting the presence of LN metastases in patients with CRC. Methods: We retrospectively reviewed the medical charts of patients who underwent curative surgery for colorectal adenocarcinoma preoperatively scheduled as stage I-II, according to the histopathology of the post-colonoscopy specimen and the results of abdominal CT-scan. Two groups of sex- and age-matched patients were randomly selected: (i) Group 1, 22 patients with LN metastases (N+), and (ii) Group 2, 24 patients with no LN metastases (N0). Overall, there were 46 patients: 28 men (60.9%), 18 women (39.1%) with a median age of 60 years (range 51-78 years). In all specimens, tissue sections of 5 μm thickness were stained using (i) three steps-indirect streptavidin method for monoclonal mouse anti-rat PCNA (considering as positive vs. negative reaction brown nuclear staining) and (ii) a biotin-free horseradish peroxidase enzyme-labeled polymer and a primary mouse monoclonal antibodies against Ki-67/clone MIB-1 (overexpression vs. non-overexpression). Results: The results are reported in the Table. Ki-67 was more sensitive (77.3% vs. 68.1%) and specific (87.5% vs. 83.3%) than PCNA. The sensitivity and accuracy of Ki-63 and PCAN together were 90.9% (χ2=7.29, p=0.007) and 91.7% (χ2=8.99, p=0.003), respectively, while the specificity did not differ significantly (χ2=1.33, p=0.25). Conclusion: In patients with CRC, the combination of Ki-67 and PCNA overexpression could accurately correlate with the presence of node metastases (N+), suggesting the need of a RT-PCR re-evaluation of a negative standard hematoxylin-eosin specimen in these patients.