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

BACKGROUND: 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.

OBJECTIVE: We assessed the impact of neoadjuvant chemotherapy (NAC) on P16INK4a expression in breast specimens.

METHODS: 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).

RESULTS: 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.

CONCLUSION: 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.