CYP3A4 and neoplasm: ICI 182,780 is metabolized via CYP3A4, which also metabolizes estradiol, suggesting one potential mechanism by which ICI 182,780 treatment might modulate estradiol levels The lack of a statistically significant difference in tumor growth with use of the estrogen receptor antagonist strongly suggests that tumor inhibition is independent of the estrogen receptor as well as androgens derived from testicular and adrenal sources.