Escape of the response to a long-acting somatostatin analogue (SMS 201–995) in patients with VIPoma

Two patients with severe secretory diarrhea due to metastatic vasoactive intestinal peptidoma were treated with a synthetic somatostatin analogue in an attempt to control the patients' vasoactive intestinal peptide-related symptoms. In both patients, a good initial response to this treatment could be demonstrated; not only did diarrhea subside but there was also a dramatic fall in vasoactive intestinal peptide plasma levels. However, after 11 and 4 days respectively, diarrhea recurred accompanied by a rise in vasoactive intestinal peptide plasma levels. In fact, under treatment with the somatostatin analogue and with natural somatostatin, a significant rebound state was observed regarding diarrhea as well as vasoactive intestinal peptide levels, which caused considerable difficulty in the clinical management in 1 patient. This patient had to undergo surgery. In the second patient, the responsiveness to somatostatin analogue returned a few days after discontinuation of the treatment, lasting, however, for a short period only. The possible mechanism of this escape and rebound with somatostatin treatment is discussed.