ESR1 and neoplasm: Examination of the association between Skp2 or p27Kip1 and patients' clinicopathological characteristics showed a strong association between Skp2 expression and loss of tumor differentiation (r = -0.400; P = 0.005), young age (r = -0.337; P = 0.022), and negative ER or negative PR status (r = -0.589; P = 0.001 and r = -0.674; P = 0.001), respectively.