Association of Somatostatin Receptor 2 Immunohistochemical Expression with [¹¹¹In]-DTPA Octreotide Scintigraphy and [⁶⁸Ga]-DOTATOC PET/CT in Neuroendocrine Tumors

Abstract

In the absence of preoperative somatostatin receptor (sst) scans, knowledge of immunohistochemical sst2 tumor expression may help predicting the success of somatostatin analogue-based follow-up studies and treatment of neuroendocrine tumors (NET). We studied the association between sst immunostaining and tracer uptake in [¹¹¹In]-DTPA octreotide (DTPAOC) scintigraphy and [⁶⁸Ga]-DOTA-d-Phe(1)-Tyr(3)-octreotide (DOTATOC) positron emission tomography (PET)/computed tomography (CT). Retrospective analy-sis of 36 NET patients was carried out. In 40 tumors, immunohistochemical sst2, sst3, and sst5 expressions were analyzed using a pathological scoring, applying monoclonal (sst2) or polyclonal antibodies (sst3, sst5). In 14 lesions, [¹¹¹In]-DTPAOC uptake was assessed by a semiquantitative score. In 26 tumors, [⁶⁸Ga]-DOTATOC PET/CT was quantified using an uptake score and maximal standard uptake value (SUV_max). Combined and separate qualitative analysis of sst scans revealed significant associations between increased tracer uptake and immunohistochemical sst2 detection (combined: ρ=0.56, p=0.0002, [¹¹¹In]-DTPAOC: ρ=0.63, p=0.0152, and [⁶⁸Ga]-DOTATOC: ρ=0.52, p=0.0065, respectively). In contrast, sst3 and sst5 immunostaining was not associated with tracer uptake (all p>0.14). The semiquantitative immunohistochemical score for sst2 was associated with the [⁶⁸Ga]-DOTATOC uptake score and SUV_max values (ρ=0.67, p=0.0002 and ρ=0.63, p=0.0010, respectively), but not with the [¹¹¹In]-DTPAOC uptake score (ρ=0.24, p=0.4). In patients without preoperative sst scans, knowledge of immunohistochemical sst2 expression may help estimating the value of sst imaging in the clinical follow-up, in particular in those lesions with positive sst2 immunostaining. Negativity for sst2, however, does not rule out tracer uptake in some patients, with heterogeneous sst2 expression within the tumor as a potential explanation.

Key words

neuroendocrine tumors - NET - sst - [⁶⁸Ga]-DOTA-Tyr-octreotide - [¹¹¹In]-DTPAOC

References

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