Cancers detected and induced in mammographic screening: new screening schedules and younger women with family history.

The numbers of cancers detected and induced in breast screening programmes are examined for two-view screening, and for a 2 year screening interval, in contrast to the single view screening at a 3 year interval of the UK Breast Screening Programme up until early 1995. Two-view screening is also considered for the 1 year interval and age range of the current UK age trial (40-47 years). The corresponding figures for screening of groups having a family history of breast cancer are calculated and discussed. Breast cancer induction data are taken from National Radiological Protection Board publications. Cancer detection rates are based on observed rates where available, and calculated rates otherwise. The results of calculations indicate cause for concern if screening is to be extended below the age of 30 years (or below 35 years in certain categories), or below 40 years of age if family history groups are shown in the future to have a generally increased susceptibility to ionizing radiation. The importance of restricting dose to 2 mGy per film (mean glandular dose for a standard breast thickness of 4.5 cm) is stressed, together with the need ot maintain maximum image quality. This is especially true for the family history groups, who should only be screened in centres within established screening programmes, or in centres with equally strict quality control procedures.