Alteration of somatostatin receptor 2 expression in canine mammary gland tumor

SAKAI, Kosei; YONEZAWA, Tomohiro; YAMAWAKI, Hideyuki; OYAMADA, Toshifumi

down-regulated in more aggressive and less differentiated benign breast tumors [5] . The results of immunohistological staining agree with these human studies [5, 8] . Protein levels of the benign tumors were also less than the normal or hyperplastic tissue, as shown by Western blotting. These findings suggest that SSTR2 deficiency in canines may contribute to the development of benign tumors. Alteration of SSTR2 expression in the MGT is not fully understood. Some studies in human breast cancer report that the SSTR2 immunohistochemical reaction was less in malignant tumors than in normal tissue, but others report the opposite relationship for SSTR2 mRNA. For instance, Reubi et al. detected SSTR2-positive immunoreactivity in only 3/39 (8%) of human malignant breast tumors [15] , while Orlando et al. performed q-PCR of 169 human breast cancers and concluded that the SSTR2 mRNA level was tremendously higher in human breast cancers than in unaffected tissues [13] . Evans et al. found SSTR2 mRNA expression in almost all breast carcinoma, but in only approximately half of benign tumors or normal breast tissues [7] . In the present study, all of SSTR2 immunohistochemical intensity in malignant tumors was lower or negative compared to normal tissues, whereas SSTR2 protein levels in two of three malignant tumors were higher than the other groups in the Western blotting analysis. Although mRNA levels were not determined in these specimens, our standings tended to be compatible with the previous results and this is the first report presenting the paradoxical results within one study.