The significance of the frequency and occurrence of breast cancer for treatment. Essential aspects of new Danish studies of the natural history of breast cancer.

The natural history of breast cancer (BC) has been evaluated by two entirely different types of consecutive and unselected materials: The general female population. Females with the breast cancer disease. The frequency of in situ carcinoma in the general female population is about 25 per cent. The growth pattern of the in situ carcinomas is predominantly microfocal contrary to findings in mammography selected surgical materials where tumor forming and/or diffuse types contribute to more than 30 per cent. Evidence is established of three different stages of the development of invasive breast carcinoma: The benign epithelial hyperplastic stage, the microfocal in situ carcinoma stage and the cancer stage. Among females with the BC-disease the residual breast glandular tissue in the contralateral breast develops a new primary invasive carcinoma in 33 per cent and furthermore in situ carcinoma in another 35 per cent. Death of disseminated metastases and axillary lymphnode metastases is significantly related to these new primaries. Residual breast glandular tissue left behind after total mastectomy contributes to new primary invasive carcinoma. Thus among clinical chest-wall recurrences not less than 20 per cent were primary invasive cancers. Our investigations have considerable impact on treatment: As concern microfocal in situ lesions they support a conservative attitude as regard treatment, providing the females are included in prospective follow-up studies including mammography. As concern the contralateral breast they support a more active attitude, but more studies are needed. Meanwhile a close follow-up program is an inevitable consequence.(ABSTRACT TRUNCATED AT 250 WORDS)