Somatostatin receptor expression in Merkel cell carcinoma as target for molecular imaging

Abstract

BackgroundMerkel cell carcinoma (MCC) is a rare cutaneous neoplasm with increasing incidence, aggressive behavior and poor prognosis. Somatostatin receptors (SSTR) are expressed in MCC and represent a potential target for both imaging and treatment.MethodsTo non-invasively assess SSTR expression in MCC using PET and the radiotracers [68Ga]DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) or -octreotate (DOTATATE) as surrogate for tumor burden. In 24 patients with histologically proven MCC SSTR-PET was performed and compared to results of computed tomography (CT).ResultsSSTR-PET detected primary and metastatic MCC lesions. On a patient-based analysis, sensitivity of SSTR-PET was 73% for nodal metastases, 100% for bone, and 67% for soft-tissue metastases, respectively. Notably, brain metastases were initially detected by SSTR-PET in 2 patients, whereas liver and lung metastases were diagnosed exclusively by CT. SSTR-PET showed concordance to CT results in 20 out of 24 patients. Four patients (17%) were up-staged due to SSTR-PET and patient management was changed in 3 patients (13%).ConclusionSSTR-PET showed high sensitivity for imaging bone, soft tissue and brain metastases, and particularly in combination with CT had a significant impact on clinical stage and patient management.

Somatostatin Receptors 2A and 5 Are Expressed in Merkel Cell Carcinoma with No Association with Disease Severity

“…In the largest series evaluating 20 patients with MCC, 111 indium-octreotide scintigraphy demonstrated a sensitivity of 78 and a specificity of 95%. However, PET/CT imaging with 68 gallium-labelled somatostatin analogues ( 68 Ga-DOTATOC, 68 Ga-DOTATATE) has greater detection efficacy in NETs [54], and recent studies have suggested its accuracy in MCC staging [18,22]. The lack of sensitivity of conventional SRI in MCC patients may be related to the heterogeneity of individual SSTR expression, as evidenced by immunohistochemistry in our study.…”

“…This is supported by the ability of SRI to detect MCCs and their metastases [17,18,19,20,21,22] as well as some cases of tumoural response to somatostatin analogues [23,24,25,26,27,28]. However, the efficacy of SSTR-targeted imaging and therapy in MCC patients is not uniform, suggesting that the in situ expression of SSTRs in MCCs may be heterogeneous.…”

Favorable Response of Metastatic Merkel Cell Carcinoma to Targeted 177Lu-DOTATATE Therapy: Will PRRT Evolve to Become an Important Approach in Receptor-Positive Cases?

“…Wide local excision with adjuvant irradiation is the usual treatment approach, with neck dissection added if there are clinically positive nodes. Contrastenhanced CT has traditionally been the standard modality for staging, but the potential of 18 F-FDG PET and somatostatin receptor-based 68 Ga-DOTANOC/TATE PET/CT for staging has also been described (4,5). In an early report (4), metastatic disease in subcentimeter-sized lymph nodes was seen on pretreatment 18 F-FDG PET/CT but not on CT, and posttreatment 18 F-FDG PET correctly depicted a response to therapy.…”

Neuroendocrine neoplasms and somatostatin receptor subtypes expression

“…Many articles bring information about SSTR expression using the nuclear medicine methods -for this knowledge we send the reader to the references [49][50][51][52][53][54].…”