True positive somatostatin receptor scintigraphy in primary breast cancer correlates with expression of sst2A and sst5

In-111-DTPA-D-Phe(1)]-octreotide scintigraphy has been shown to reveal somatostatin receptor-positive lesions in the majority of primary breast cancers. We have recently developed a panel of somatostatin receptor subtype-specific antibodies that effectively stain formalin-fixed, paraffin-embedded breast cancer tissue. However, it is uncertain to what extend somatostatin receptors detected during immunohistochemical staining represent functional binding sites responsible for high tracer uptake during somatostatin receptor scintigraphy. Patients and methods. We, therefore, conducted a prospective study in which 23 patients with suspected breast tumors were included. All patients received [In-111]-pentetreotide scintigraphy. After surgical removal of the tumor, the somatostatin receptor status was determined by immunohistochemistry. Results. Among 20 pathologically proven malignant tumors (14 ductal and six lobular carcinomas), 13 ( similar to65%) were scintigraphically visible. Of the 20 primary breast cancer specimens analyzed, three tumors (similar to15%) were positive for sst(1), nine(similar to45%) revealed immunoreactive sst(2A) receptors, eight (similar to40%) showed sst(3)-like immunoreactivity, and 14 (similar to70%) were positive for sst(5). There was an excellent correlation between the outcome of somatostatin receptor scintigraphy and expression of sst(2A) (P = 0.025) as well as sst(5) (P = 0.001) but not expression of either sst(1) (P = 0.343) or sst(3) (P = 0.400). Conclusion. Both sst(2A) and sst(5) can be responsible for high tracer uptake during [In-111]-pentetreotide scintigraphy in primary breast cancer. Thus, somatostatin receptor scintigraphy may possibly be of value in the detection of proven somatostatin receptor sst(2A)- and/or sst(5)-positive lesions in metastatic breast cancer.