Expression of GHRH-R, a Potentially Targetable Biomarker, in Triple-negative Breast Cancer

Purpose: Growth hormone-releasing hormone (GHRH) has been shown to modify the growth behavior of many cancers, including breast. GHRH is produced by tumor cells, acts in an autocrine/paracrine manner, and requires the presence of GHRH receptor (GHRH-R) on the tumor cells to exert its effects. GHRH activity can be effectively blocked by synthetic antagonists of its receptor and hence, the expression of GHRH-R by tumor cells could serve as a predictor of response to GHRH-R antagonist therapy. In this study, we investigated the expression of GHRH-R in triple-negative breast cancers (TNBC). As TNBCs are morphologically and immunophenotypically heterogenous, the staining results were also correlated with the histologic subtypes of these tumors. Materials and Methods: On the basis of histomorphology and immunophenotype, 134 cases of primary TNBCs were further subdivided into medullary, metaplastic, apocrine, and invasive ductal carcinomas of no special type (IDC-NST). Immunohistochemistry for GHRH-R was performed on paraffin sections and the staining results were assessed semiquantitatively as negative, low expression, moderate, and high expression. Results: Of the 134 TNBCs, 85 were classified as IDC-NST, 25 as metaplastic, 16 as medullary, and 8 as apocrine carcinoma. Overall, positive reaction for GHRH-R was seen in 77 (57%) of tumors including 66 (77.6%) of IDC-NST. All medullary carcinomas were negative for GHRH-R and, with the exception of 1 case with low expression, none of the metaplastic carcinomas expressed GHRH-R (P<0.005). Conclusions: A considerable number of TNBCs are positive for GHRH-R as a predictor of potential response to anti-GHRH-R treatment. This expression however, varies considerably between histologic subtypes of triple-negative breast cancers. Although most medullary and metaplastic carcinomas do not express GHRH-R, three fourths of the IDC-NST show a positive reaction. Testing for GHRH-R expression is therefore advisable if anti-GHRH-R therapy is being considered.