The association between blood type A and breast cancer was evaluated in 648 patients with family histories of the disease, 1897 unselected patients, 4577 institutional blood donor controls, and 14,508 extramural blood donor controls. The familial patients were classified into three pedigree groups in which the lifetime breast cancer risks to first‐degree relatives ranged from 11% to 32%. In the pedigree group associated with a relatively low risk to relatives, the authors saw a significant excess of blood type A individuals when compared with either control group. The unselected patient population, which was considered to refer to a general series of patients, also showed an excess of blood type A individuals with either control but a significant excess only in comparison with institutional controls. Patients from high‐risk pedigrees with inherited forms of breast cancer showed no association when compared with either control group. The effect of blood type A on breast cancer risk was considered too small to be of use in identifying women at high risk. The results further suggested that the effect of blood type A on breast cancer development was capable of being masked by the effect of breast cancer susceptibility genes and/or that the inherited and noninherited types involve different etiologic mechanisms.
The risk of other cancers in relatives of retinoblastoma (RTB) patients was determined by a survey of the mortality experience of siblings, parents, parental siblings, and grandparents of all U.S. or Canadian RTB patients referred to The University of Texas M.D. Anderson Hospital and Tumor Institute between 1944 and 1980. Expected mortality was ascertained by the application of age-, sex-, race-, and calendar year-specific U.S. mortality rates to the observed person-years. Among 607 relatives of 33 unilateral-sporadic RTB probands, no excess in cancer deaths was observed (observed/expected = 18/22). Among 733 relatives of 47 bilateral-familial RTB probands, a slight excess in cancer deaths was observed (41/31). A significant excess in cancer deaths was occurred in relatives under age 55 years (18/9) and in fathers (7/1) of the bilateral RTB probands. To determine whether the cancer excess was related to some unique allele associated with second tumors in RTB survivors, the cancer mortality of 203 relatives of the 14 RTB patients with second tumors was examined, and no excess was observed (11/11). To determine whether the excess might be attributable to an unexpressed RTB gene or precursor, the mortality experience was examined in 6 kindreds in which parents, unaffected by RTB, had more than 1 child with RTB. Among these 72 relatives a significant excess in cancer deaths was observed (8/2). The findings demonstrate a modest overall cancer excess in relatives of hereditary RTB patients and suggest it may be attributable to an unexpressed RTB gene or precursor in a small number of kindreds. Mechanisms for an apparent "precursor" might involve a delayed mutation, genetic mosaicism, or a submicroscopic balanced chromosomal translocation.
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