Radiotherapy with a Radiolabeled Somatostatin Analogue, [lllIn-DTPA-~-Phel] -0ctreo tide A Case History

In 1987, we started octreotide receptor scintigraphy in humans. After a few years of using the radioiodinated [Tyrs]-octreotide,' we switched to [lllIn-DTPA-~-Phe*]octreotide, which has many advantages over the radioiodinated Patients with various forms of cancer, both classically known as neuroendocrine and nonendocrine, have been inve~tigated.~ The application of these new peptide-receptor agents in scintigraphy, and of many others that will become available in the near future, such as substance P and bombesin or their derivatives, might evoke a combination of optimism and pessimism. After all, the presence of receptors determines the possibility of detecting the abnormality or tumor by peptide receptor scintigraphy (PRS). Thus, the classical concept of false positives and false negatives really is not applicable to visualization by means of PRS.' This technique primarily allows an interpretation with regard to receptor presence and not to anatomical abnormalities, as is the case with CT, ultrasound, and MRI. Only at a second stage, after showing the localization of an abnormal density of receptors, one might conclude the presence of an anatomical abnormality expressing the peptide receptors, for example, a primary pancreatic islet cell tumor expressing somatostatin receptors. However, when PRS does not demonstrate (a) lesion(s), suggesting that a tumor or (several of the) metastases do not express (anymore) a certain peptide receptor, this also might be of paramount importance with regard to therapeutic advice to the patient. Dedifferentiation of a tumor is accompanied by loss of a given peptide receptor, and this information influences the oncologist's therapeutic decisions. An example is the choice between the use of somatostatin analogues or cytostatic drugs in patients with neuroendocrine tumors that are well differentiated or have become anaplastic, respectively.6*' With future (radio)therapy using (radio)labeled peptide(-derivatives), the presence (in the individual patient!) of several undifferentiated metastases, that do not bind a given (radio)ligand as opposed to the well-differentiated metastases, necessitates (an)