Familial association of colorectal adenocarcinoma with cancers at other sites.

Data on the familial associations of colorectal cancer (CRC) of adenocarcinoma histology are limited, but they are of interest because they may give us clues about as yet unknown family clusters. We calculated standardised incidence ratios (SIRs) for right- and left-sided colon cancer and rectal cancer in offspring using data from the Swedish Family-Cancer Database covering familial tumours from 1991 to 2000. The offspring were at an increased risk of developing colon adenocarcinoma when parents presented with CRC (SIR 1.81), endometrial (SIR 1.52) and kidney (SIR 1.42) cancers. The SIRs in siblings were increased when a co-sibling was diagnosed with CRC (SIR 3.26), myeloma (SIR 2.65) and leukaemia (SIR 2.53). Right-sided colon cancer was associated with familial pancreatic, squamous cell skin cancers, thyroid gland cancer and Hodgkin's disease. Left-sided colon cancer was associated with testicular cancers. Rectal cancer was associated with cervical and genital cancers in mothers. Most of the findings were consistent with data on known cancer syndromes. A new association was noted where rectal cancer in offspring was related to cervical and female genital cancers in mothers through an unknown mechanism. Hodgkin's disease and myeloma were also associated with right-sided colon cancer in offspring. The association with carcinoma of the testis, renal parenchyma, skin and leukaemia need to be confirmed in an independent series.