Indium-111 octreotide scintigraphy of Merkel cell carcinomas and their metastases

Somatostatin receptor scintigraphy (SRS) may be of interest for staging Merkel Cell Carcinoma (MCC). This study was undertaken to evaluate the sensitivity and specificity of SRS and to determine its role compared to conventional investigations.

From 1993 to December 2000, 20 patients (10 females and 10 males, aged from 38 to 88, mean 66 years) were included prospectively. At the time of SRS: 12 patients had been diagnosed as having stage I disease, 6 stage II and 4 stage III. Two patients had two SRS studies during the course of their disease. SRS was performed with Indium-111 pentetreotide (Octreoscan), a radiolabelled somatostatin analogue. Patients were treated according to the clinical stage. A regular follow-up was scheduled every three months.

SRS depicted stage I and II MCC tumour sites with an overall sensitivity of 78% (95% confidence interval (CI): 40%-97%) and a specificity of 96% (81%-100%). The histopathological diagnosis was used as the gold standard. Sites visualised by SRS were compared to those detected with conventional modalities and to follow-up data for all stages: SRS visualised four out of five primary tumour sites, six out of eight lymph node sites, no skin metastases (14 sites in 2 patients), two out of three thoracic metastases and zero out of two hepatic metastases. SRS did not influence treatment decision-making in any of the cases.

Although SRS seems highly specific in MCC and could be of help in difficult cases, it cannot be recommended for routine evaluation.