Somatostatin and cancer.

The potential role of somatostatin (SRIF) in the diagnosis and treatment of nonendocrine human cancers is reviewed. There have been many reports of the growth-inhibitory activity of SRIF on normal and transformed cells in vitro. Many processes involved in malignant tumor growth depend on autocrine growth mechanisms, and somatostatin receptors (ssts) are present on many human cancers. It is possible that mutations in ssts result in a loss of check on proliferation in cancer cells. SRIF analogs may have a number of roles in clinical oncology. Use of radiolabeled tracers enables imaging of tumors bearing ssts; newer agents may enable positron emission tomography (PET) analyses or may be used to deliver lethal radiation doses to cells bearing a unique subset of sst. Although the ability of SRIF and its analogs to inhibit cellular proliferation has been shown in vitro, it has yet to be demonstrated in humans with cancer. Clinical improvements seen with SRIF or its analogs in cancer patients may be related to indirect effects, such as pain relief, reduction of gastrointestinal side effects of chemotherapeutic agents, effects on local production of growth factors, and inhibition of tumoral angiogenesis. Thus, with regard to their potential therapeutic role, SRIF analogs are likely to be used only in conjunction with other approaches, such as radiation, immunotherapy, chemotherapy, and growth factor modulation. Further research into the fundamental functions of each of the ssts and the intracellular actions of SRIF analogs will be needed to assess the potential usefulness of the latter in slowing the progression of human cancers.