Discloses an in vitro method of predicting the efficacy of one or more anti-progestin(s) on a tumour or suspected tumour comprising: a) identifying progesterone receptor positive cells in a tissue sample suspected of being tumorigenic or cancerous from a patient b) determining the degree of focal distribution of the progesterone receptor in nuclei of the progesterone positive cells from the tissue sample and c) determining whether the degree of focal distribution in the tissue sample is greater than about 5% of the progesterone receptor positive cells. Also discloses related use of an anti-progestin composition in the manufacture of a medicament for treating a tumour susceptible to growth inhibition by one or more anti-progestin, a method of screening a drug candidate for the ability to decrease focal distribution of the nuclear progesterone receptor, and a system for classifying a tumour as being susceptible for treatment with an anti-progestin.
