Somatostatin receptor scintigraphy is useful in diagnosing
tumors with increased expression of
somatostatin receptors. The correct use of this technique reveals the localization of neuroendocrine primary
tumors and unknown
metastases in approximately 90% of patients. However,
somatostatin receptor scintigraphy also can image many other human
tumors expressing
somatostatin receptors, including
malignant lymphomas and
thymomas. The sensitivity of
somatostatin receptor scintigraphy to image
somatostatin receptor-positive
tumors is very high, but due to the variable expression of specific receptor subtypes, the specificity can be relatively low. This drawback is crucial in evaluating lymphoproliferative diseases, or, in general, when immune cells are involved. The sensitivity of
somatostatin receptor scintigraphy for
Hodgkin's lymphoma is 95%-100%, whereas for
non-Hodgkin's lymphoma it is around 80%. It has been shown that the uptake of [(111)In-
DTPA(0)]
octreotide in
lymphomas is lower compared to the uptake in
neuroendocrine tumors. This is mainly attributed to the low number of receptors on immune cells compared to neuroendocrine cells; however,
ligand-induced internalization and differential receptor regulation may also participate in determining this phenomenon. Therefore, caution should be taken when interpreting data from some studies. Several new
ligands are currently under study to improve these limits and the expression of other
neuropeptide receptors is being investigated to provide a molecular basis for in vivo multireceptor targeting of
tumors. With the use of currently available
somatostatin analogs,
somatostatin receptor scintigraphy does not seem to have a significant impact in patients with
lymphomas for diagnostic purposes. There are a few exceptions, however. Among these, the staging and restaging of extragastric
lymphoma MALT-type may present some advantages. Conversely,
somatostatin receptor scintigraphy in the imaging of thymic
malignancies could enhance both our diagnostic and therapeutic capabilities.
Somatostatin receptor scintigraphy is diagnostically relevant in differentiating malignant from benign lesions, especially in those patients with associated
paraneoplastic syndromes, and is the main criterion to select patients suitable for
therapy with
somatostatin analogs. Recent findings emerging from in vitro studies on
somatostatin receptor physiology in immune cells will certainly reopen and expand the potential applications of
somatostatin analogs for in vivo diagnostic and therapeutic options.