The present invention relates to methods for the stratification of individuals suffering from cancer. In particular, the present invention relates to the finding that PTA-fragments allow the discrimination of cancer cells being susceptible to an anti-endocrine therapy from cancer cells not susceptible to said therapy. Thus, PTA-fragments can be a surrogate for estradiol receptor detection by immune histology, can be a marker to monitor resistance of cancer cells towards anti-estradiol therapy, can be used to monitor rezidives and can be used to determine the status of dedifferentiation, e.g. the state of cancer cells. PTA-fragments have the advantage to be determined from easily accessible patient samples such as serum or plasma. The present invention further encompasses specific PTA peptides and nucleic acids, antibodies therefore, test kits and diagnostic and therapeutic methods and compositions.