Evaluation of the expression of P16INK4A by immunohistochemistry in post-neoadjuvant chemotherapy hormone receptor negative breast cancer specimens.

Abstract

Hormone-receptor-negative breast carcinoma (HRNBC), including triple-negative and HER-2 amplified tumors, can overexpress P16INK4a with substantial contribution to tumor progression. In nonneoplastic cells, P16INK4a mediates growth arrest and senescence secondary to cytotoxic compounds. We assessed the impact of neoadjuvant chemotherapy (NAC) on P16INK4a expression in breast specimens. P16INK4a and CD-44 were evaluated by immunohistochemistry in biopsies and subsequent post-NAC excision in a cohort of 27 women with HRNBC. Positivity was estimated on hotspots of tissue available by calculating cellular densities in nonneoplastic tissues with a low proliferation rate (Ki-67 < 1%) and tumor percentage using ImageJ 1.51t (National Institutes of Health, USA). Pre-NAC P16INK4a and CD-44 tumor expression were similar between the complete (n =15) and incomplete (n =12) response groups. Residual HRNBCs exhibited decreased immunoreactivity for P16INK4a, while the expression of CD-44 increased (n =10, P <0.05). The magnitude of change correlated with the baseline expression (r =0.37, P16; r = -0.85, CD-44). Post-NAC nonneoplastic mammary duct and lobular epithelia, perilobular stroma, and adipose tissue, but not peritumoral stroma, accumulated P16INK4a(+) cells. The post-NAC cellular density change was more significant in epithelia of patients with high P16INK4a(+) baseline (r =0.86, P <0.0001) and those with a complete pathologic response (n =14, P <0.05). All tumors beds with complete treatment effect showed diffuse P16INK4a positivity. NAC induced the accumulation of P16INK4a(+)cells in nonneoplastic breast tissues more pronounced in patients with a complete pathologic response. Therapy-induced senescence is a potential marker of bystander damage due to NAC. P16INK4a loss and CD-44 gain may represent a phenotype of chemoresistance in residual HRNBCs.