Calculated concordance rates for leukemia in identical twin children
Method of ascertainment . | No. pairs (infants)* . | Concordance rate, %† . | Reference . |
|---|---|---|---|
| Regional vital statistics (death certificates); 1947-1960 plus 3 clinical case series, 1954-1962 (US) | 5 (2) | 25 | MacMahon and Levy22 |
| Nationwide vital statistics survey, 1960-1967 (US) | 7 (3) | 17 | Miller24 |
| Twin database plus clinical trial databases (US/United Kingdom) | 4 (1) | 5-10‡ | Buckley et al34 |
| Cancer registry, 1958-1998 (Sweden) | 3 (0) | 15 | Hemminki and Jiang138 |
| Nationwide clinical database, 1972-1998 (The Netherlands) | 2 (0) | 26 | § |
Method of ascertainment . | No. pairs (infants)* . | Concordance rate, %† . | Reference . |
|---|---|---|---|
| Regional vital statistics (death certificates); 1947-1960 plus 3 clinical case series, 1954-1962 (US) | 5 (2) | 25 | MacMahon and Levy22 |
| Nationwide vital statistics survey, 1960-1967 (US) | 7 (3) | 17 | Miller24 |
| Twin database plus clinical trial databases (US/United Kingdom) | 4 (1) | 5-10‡ | Buckley et al34 |
| Cancer registry, 1958-1998 (Sweden) | 3 (0) | 15 | Hemminki and Jiang138 |
| Nationwide clinical database, 1972-1998 (The Netherlands) | 2 (0) | 26 | § |
Number of concordant pairs documented and used to calculate rate. In parentheses, the number of concordant pairs that were diagnosed as infants (<12 months). The differential diagnosis in these cases was ALL (in 10), AML (in 3), and acute leukemia of uncertain subtype in the rest.
The calculation of concordance rate depends on how cases are ascertained. If twins in a pair are identified independently, for example, via a cancer registry database, then the rate is considered “casewise” (as opposed to “pairwise” if detection of one case leads to identification of the other). A casewise rate in essence computes the risk of a second twin having leukemia if one twin is known to be affected.
Concordance rate varied according to whether all cases incompletely followed up were included and in relation to age cut-off point.
Unpublished data (E. van Wering and M. G., June 1999). We have calculated this casewise rate. Two pairs of twins with concordant ALL were referred to the LRF Twin Survey (see “Triplets with ALL”); these were the only concordant twins documented in the period 1972 to 1998 in the comprehensive Dutch Childhood Leukemia Study Group database in which there were 11 identical twins with discordant ALL (ie, only one twin affected).