Hormone receptors, ploidy and proliferation rate in breast cancers up to 10 mm.

A total of 191 malignant mammary lesions of 10 mm or less in diameter have been analysed with regard to hormone receptor content (107 of 179) and ploidy (112 of 191) in a repeated mammography screening population (second to fourth screening round). Forty-eight per cent were diploid and 68% oestrogen receptor-positive. Mean proliferation rate, calculated as S-phase fraction (SPF), was 6.2 +/- 5.0. Significantly lower SPF was observed in diploid tumours. In very small tumours (less than or equal to 5 mm) SPF was higher as was the fraction of receptor-negative tumours. Among these small cancers a hypothetical high-risk group with SPF greater than or equal to 10% and receptor-negativity will contain 7% of the patients. If SPF and receptor content are chosen as prognostic factors, the latter patients may be a group suitable for adjuvant therapy in treatment schedules.