IMMUNOCYTOCHEMICAL DETECTION OF SOMATOSTATIN RECEPTORS SST(1), SST(2A), SST(2B), AND SST(3) IN PARAFFIN-EMBEDDED BREAST-CANCER TISSUE USINGSUBTYPE-SPECIFIC ANTIBODIES

The long-acting somatostatin analogue octreotide (SMS 201-995) inhibit s growth of certain breast cancer cell lines ipl vivo and in vitro. Be cause the antiproliferative action of octreotide depends on at Least t he presence of somatostatin receptors, it is crucial to determine the pattern of somatostatin receptor protein expression on the tumor cells , In the present study, we have raised polyclonal antibodies to somato statin receptor subtypes (ssts) sst(1), sst(2A), sst(2B), and sst(3) u sing peptides corresponding to their COOH-terminal sequences. These an tisera were used for immunocytochemical staining of paraffin sections of 33 primary breast cancers. Somatostatin receptor-like immunoreactiv ity (Li) was predominantly localized to the plasma membrane of the tum or cells, In the vest majority of positively stained tumors, somatosta tin receptor-ii was uniformly present on nearly all tumor cells, Both the level and the pattern of expression of ssts varied greatly between individual carcinomas. sst(2A)-li and/or sst(2B)-Li was detectable in 28 tumors (85%); among these, 14 tumors (42%) showed particularly hig h levels of sst(2)-Li, sst(1)-Li was found in 17 (52%) cases and sst(3 )-Li in 16 (48%) cases. The expression of ssts was independent of pati ent age, menopausal status, diagnosis, histological grade, and levels of estrogen and progesterone receptors, The immunocytochemical determi nation of somatostatin receptor status allows direct detection of rece ptor protein on the tumor cells and, hence, may provide more precise i nformation than reverse transcription-PCR for predicting response to o ctreotide therapy in breast cancer.