The answer is C. p53.
Mutations of the p53 gene are associated with malignancies, and research suggests that the mutation may increase the risk of chemotherapy resistance.
A is not correct because NRAS mutations play a role in the development of a variety of cancers and most notably increase the risk of breast and ovarian cancer. However, the mutation has not shown to positively or negatively affect response to chemotherapy.
B is not correct because APC gene mutations increase the likelihood of developing colorectal cancer but have not shown any effect on chemotherapy response.
D is not correct because the presence of a mutation to the VHL (Von-Hippel-Landau) gene will allow abnormal cell growth and division, leading to remarkably higher cancer rates, but has not demonstrated a significant impact on response to treatment.