Multiple primary cancers of breast and cervix uteri: an epidemiological approach to analysis.

Index sites of breast and cervix uteri were selected from populationbased data held at the West Midlands and Birmingham Regional Cancer Registry, and the expected numbers of second primary cancers in cervix and breast were computed (sequence analyses). In the breast series (17,756 patients) a small deficit of cervical tumours was observed (O = 16, E = 2·119, O/E = 0·76, P > 0·05), while in the cervix series (4817 patients) a small excess of breast tumours was found (O = 29, E = 23·38, O/E = 1·24, P > 0·05) over a period of 15 years.A theoretical statement of the combined risk of the 2 tumours occurring in the same individual of a general population was developed and was compared with the practical approach of summing the sequence analyses (complementary analysis). Complementary analysis indicated that there was no excess of women with the 2 primary tumours (O = 45, E = 44·57, O/E = 1·01) and that cancers of the breast and cervix uteri are not aetiologically related.