True Positive Somatostatin Receptor Scintigraphy in Primary Breast Cancer Correlates with Expression of sst2A and sst5

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Abstract
[111 In-DTPA-D-Phe1]-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 [111In]-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 (∼65%) were scintigraphically visible. Of the 20 primary breast cancer specimens analyzed, three tumors (∼15%) were positive for sst1, nine (∼45%) revealed immunoreactive sst2A receptors, eight (∼40%) showed sst3-like immunoreactivity, and 14 (∼70%) were positive for sst5. There was an excellent correlation between the outcome of somatostatin receptor scintigraphy and expression of sst2A (P = 0.025) as well as sst5 (P < 0.001) but not expression of either sst1 (P = 0.343) or sst3 (P = 0.400). Conclusion. Both sst2A and sst5 can be responsible for high tracer uptake during [111In]-pentetreotide scintigraphy in primary breast cancer. Thus, somatostatin receptor scintigraphy may possibly be of value in the detection of proven somatostatin receptor sst2A- and/or sst5-positive lesions in metastatic breast cancer.

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