Table 1 shows the total numbers of offspring with cancer and the numbers of familial cases in the offspring generation stratified by parents’ age at diagnosis. Depending on cancer site, some 35-81% of familial cancers in parents were diagnosed after the age of 69 (colorectal: 59% (1528/2596), lung: 56% (621/1113), breast 41% (2275/5526), prostate: 75% (4146/5555, urinary bladder: 62% (270/437), and skin cancer: 81% (268/330), melanoma: 35% (241/687), and non-Hodgkin’s lymphoma: 54% (111/205)). There were 3
917 mothers available in our sample for this study with mean birth year of 1944 (SD 22.2; median 1946; range: 1880-1994) and 3
986 fathers with mean birth year of 1941 (SD 22.7; median 1944; range 1867-1993). The figure shows a schematic representation of demographics.[f1] Parents were born from 1867 to 1993 and offspring were born from 1932 to 2008. In this study, follow-up was started from 1961 and ended at 2008 as described before.
Table 1 Total number of cases of cancer in offspring (including familial cases) by age of offspring at diagnosis and number of familial cancer cases in which parents were affected with concordant cancer
Study population and follow-up. Shaded area represents parent generation; dotted shaded area represents offspring generation
Table 2 shows the risks of concordant cancer in offspring, stratified by offspring and parental age at diagnosis. The highest familial risk was seen in patients whose parents received a diagnosis at earlier ages. Even when parents were affected in old age (≥70) the risks of concordant cancer in their offspring were significantly higher than those whose parents were not affected with the same cancer. For instance, if parents were affected at age 80-89, the hazard ratios were significantly increased in offspring for melanoma (2.3, 95% confidence interval 1.9 to 2.8), skin squamous cell carcinoma (2.0, 1.7 to 2.4), prostate (1.9, 1.8 to 2.0), non-Hodgkin’s lymphoma (1.7, 1.3 to 2.3), urinary bladder (1.9, 1.5 to 2.3), lung (1.8, 1.6 to 2.1), breast (1.6, 1.5 to 1.7), and colorectal cancer (1.6, 1.4 to 1.7). In those whose parents were diagnosed at age ≥90, the hazard ratios were still significantly increased for skin squamous cell carcinoma (1.9, 1.4 to 2.7), colorectal (1.6, 1.2 to 2.0), breast (1.3, 1.0 to 1.6), and prostate cancer (1.3, (1.1 to 1.6) (table 2).
Table 2 Risk of cancer in offspring whose parents were affected with concordant cancer compared with offspring without affected parents. Figures are hazard ratios* (95% confidence interval)
Table 2 also shows the familial hazard ratios by offspring age at diagnosis (<60 and 60-76). In offspring aged 60-76 at diagnosis, none of those with colorectal, prostate, urinary bladder, skin cancer, and non-Hodgkin’s lymphoma and melanoma had a parent affected at young age (<40) (table 1). We found no significantly increased risks for any of the cancers for offspring who received a diagnosis at older ages (60-76) whose parents were affected at young ages (<50), with the exception of breast cancer.
The absolute risks of familial cancers could be estimated based on the cumulative risks of cancers by age 75 in the Swedish population.9
The cumulative risk for colorectal cancer was 3.4%, thus a hazard ratio of 1.9 for familial colorectal cancer in offspring aged 0-76 (table 2) would be translated to a cumulative risk of 6.4%. The respective absolute risk for the other familial cancers when parents received a diagnosis at any age would be 5.0% for lung, 8.8% for breast, 30.1% for prostate, 2.8% for urinary bladder, 3.5% for skin squamous cell carcinoma, 4.6% for melanoma, and 1.6% for non-Hodgkin’s lymphoma (adjusted for the background cumulative risks of these cancers by age 75, which were 3.4% for colorectal, 2.4% for lung, 4.4% for breast, 13.1% for prostate, 1.4% for urinary bladder, 1.2% for skin cancer, 1.6% for melanoma, and 0.9% for non-Hodgkin’s lymphoma).9