Cancer mortality in relatives of retinoblastoma patients.

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.