B7-H3 and B7-H4 expression in phyllodes tumors of the breast detected by RNA in situ hybridization and immunohistochemistry: Association with clinicopathological features and T-cell infiltration.

Phyllodes tumors are rare biphasic breast tumors with the potential for both local recurrence and distant metastasis. The aberrant expression of B7-H3 and B7-H4 B7 molecules could be potential targets for future development of immunotherapeutic approaches. This work was undertaken to evaluate the expression of B7-H3 and B7-H4 in phyllodes tumors and assess the association with the grade and clinical behavior of phyllodes tumors. In addition, the roles of B7-H3 and B7-H4 in the regulation of tumor immune surveillance were evaluated by assessing the relationship between B7-H3/B7-H4 expression and T-cell infiltration. The messenger RNA and protein expression of B7-H3/B7-H4 were determined by RNAscope in situ hybridization and immunohistochemistry, respectively, in 101 phyllodes tumors (60 benign, 26 borderline, and 15 malignant) using a tissue microarray. Immunohistochemistry for CD3 and CD8 was also performed. B7-H3 messenger RNA and protein appeared to be concentrated mainly in the stromal compartment of phyllodes tumors. However, B7-H4 messenger RNA and protein were undetectable in the stromal compartment of phyllodes tumors. Stromal B7-H3 messenger RNA and protein expression were noted in 10 (16.7%) and 31 (51.7%) of 60 benign phyllodes tumors, 12 (46.1%) and 20 (76.9%) of 26 borderline phyllodes tumors, and 10 (66.7%) and 13 (86.7%) of 15 malignant phyllodes tumors, respectively. Stromal B7-H3 messenger RNA and protein expression increased as phyllodes tumors progressed from benign to borderline and finally to the malignant grade (Pearson's R = 0.411, p < 0.001 and Pearson's R = 0.293, p = 0.003, respectively). The recurrence rate was higher in the stromal B7-H3 messenger RNA or protein-positive group than in the negative group, but this difference was not significant. Stromal B7-H3 protein expression inversely correlated with the densities of CD3+ and CD8+ T-cell infiltrates ( p = 0.001 and p = 0.027, respectively). These results suggest that B7-H3 is involved in the progression of phyllodes tumors and may contribute to their immune surveillance.