Recorded quadrant incidence of female breast cancer in Great Britain suggests a disproportionate increase in the upper outer quadrant of the breast.

BACKGROUND The upper outer quadrant (UOQ) of the breast is the most frequent site for incidence of breast cancer, but the reported disproportionate incidence in this quadrant appears to rise with year of publication. MATERIALS AND METHODS In order to determine whether this increasing incidence in the UOQ is an artifact of different study populations or is chronological, data have been analysed for annual quadrant incidence of female breast cancer recorded nationally in England and Wales between 1979 and 2000 and in Scotland between 1980 and 2001. RESULTS In England and Wales, the recorded incidence of female breast cancer in the UOQ rose from 47.9% in 1979 to 53.3% in 2000, and has done so linearly over time with a correlation coefficient R of +0.71 +/- SD 0.01 (p < 0.001). Analysis of independent data from Scotland showed a similar trend in that recorded female breast cancer had also increased in the UOQ from 38.3% in 1980 to 54.7% in 2001, with a correlation coefficient R for the linear annual increase of +0.80 +/- SD 0.03 (p < 0.001). CONCLUSION These results are inconsistent with current views that the high level of UOQ breast cancer is due solely to a greater amount of target epithelial tissue in that region. Identification of the reasons for such a disproportionate site-specific increase could provide clues as to causative factors in breast cancer.