Relationship between somatostatin receptor subtype expression and clinicopathology, Ki-67, Bcl-2 and p53 in colorectal cancer.

Aim: To study the SSTR1, 2, 3, 4, 5 expression and their relationships with clinico-pathological factors, cell proliferation, Bcl-2 and p53 expression in colorectal cancer cells.

Methods: Immunohistochemical staining of five SSTR subtypes, Ki-67, Bcl-2 and p53 was performed by the standard streptavidin-peroxidase (SP) technique for the paraffin sections of 127 colorectal cancers. and expression of five SSTR subtypes in 40 specimens of normal colorectal mucosae was detected with the same method.

Results: Positive staining for five SSTR subtypes was observed in colorectal cancer cells and normal colorectal mucosae. SSTR1 was the most predominant subtype in both colorectal cancer and normal colorectal mucosa, and the second was SSTR5 or SSTR2. As compared with normal colorectal mucosa, SSTR4 was more frequently expressed in colorectal cancer cells (2.5% vs 18.9%, P<0.05); the expression of SSTR2, 4, 5 in moderately to well differentiated colorectal adenocarcinoma was significantly higher than that in poorly differentiated ones (P<0.05), the SSTR1 expression in colorectal cancer with positive lymph node metastasis was significantly higher than that with negative lymph node metastasis (72.2% and 54.5%,P<0.05). In addition, in the ulcerative type of colorectal cancer, SSTR2 expression was obviously decreased (P<0.05); the correlation did not reach a statistical significance between the five SSTR subtypes expression and Dukes'stages (P>0.05), but the frequency of SSTR1 expression increased with Dukes'stage, while SSTR3 and SSTR5 expression decreased with Dukes' stage. Moreover, there was no correlation between expression of the five SSTR subtypes and other clinicopathological factors such as age, sex, tumor site, tumor depth, distant metastasis. The proliferative indexes in colorectal cancer cells with negative expression of SSTR2 and SSTR3 were significantly higher than that with positive expression (P<0.05). The Bcl-2 expression in colorectal cancer cells with positive expression of SSTR1, 2, 3, 5 was significantly lower than that with negative expression (P<0.05). There was no correlation between five SSTR subtypes and p53 expression.

Conclusion: The most predominant SSTR subtype is SSTR1, and the second is SSTR2 or SSTR5. Five SSTR subtypes play different roles in the development of colorectal cancer. SSTR2 and SSTR3 can inhibit the proliferation and promote apoptosis of tumor cells.