Editor—Familial tendencies have previously been observed for congenital pyloric stenosis, endometriosis, and breast cancer. These conditions have never been considered to have shared aetiological origins and consequently no previous attempts have been made to investigate an association. For example, when obtaining family history information for a child with pyloric stenosis, one would not routinely request a description of adult onset conditions such as endometriosis or breast cancer. Two families sharing an unusual clustering of these three conditions (pyloric stenosis, endometriosis, and breast cancer) were ascertained at the familial cancer clinics of the Women's College and Princess Margaret Hospitals in Toronto.

Family 1 (fig 1) contains four confirmed cases of breast cancer (below age 60), seven cases of endometriosis, five cases of congenital pyloric stenosis, nine cases of polycystic ovaries, and four cases of non-insulin dependent diabetes. In a second unrelated family, a woman previously diagnosed …