NEW MATERIAL: An affinity label consists of a ligand which is specific and irreversible to a steroid hormone receptor. The label is composed of an estrogen complex constituted by an estradiol derivative which is complexed with an organometallic compound at the 17α-position of estradiol. In the affinity label, PK which measures an equilibrium constant between an alcohol at the 17β-position of the complex and carbenium forms at 17-position is negative.

EXAMPLE: 17α-Pherocenyl-17β-estradiol of formula I.

USE: Drugs for hormone radiotherapy of hormone dependent cancer, contrast medium for hormone dependent cancer.

PROCESS: For example, a compound of formula II which is prepared by silylating estrone with dimethyl-tert-butylchlorosilane is added with the lithium derivative of pherocene of formula III to obtain the compound of EXAMPLE.