Endogenous peroxidase: an alternative to oestrogen receptor in the management of breast cancer?

MANY WORKERS have shown that human breast cancers which contain oestrogen receptors (RE) are more likely to respond to hormonal therapy than those which do not (McGuire et al., 1978). RE status, as determined by conventional techniques is a relatively poor indicator of responsiveness to hormonal therapies; only 35-63% of patients classified as RE+ respond to endocrine ablation (Roberts et al., 1978; McGuire et al., 1978). Standard RE assay techniques require up to 300 mg of tumour, an amount which is often unavailable in cases presenting early with small primary tumours, or where metastatic deposits are inaccessible to open biopsy (e.g. in bone or liver). These limitations reduce the clinical usefulness of RE assays and have led to a search for alternative indicators of hormone responsiveness which might discriminate better and be detected in smaller tumour samples. Progestogen receptor (RP) (McGuire et al., 1978) and endogenous peroxidase (Lyttle & De Sombre, 1977; Duffy & Duffy, 1977; De Sombre et al., 1975) are two proteins which have been suggested as potential indicators of hormone responsiveness. The present study was set up to assess the value of endogenous peroxidase as an indicator of hormone dependence by measuring peroxidase levels in rat maummary tumours which serve as models of hormone-dependent and -independent growth. DMBA-induced rat mammary tumours are considered to serve as models of ovaryAccepted 7 December 1979