Table 3. Risk of stomach cancer associated with radiation dose by characteristics at testicular cancer diagnosis and other variablesa , b.
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RT dose <25 Gy (Ref) |
RT dose ⩾25 Gy |
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|---|---|---|---|---|---|---|---|---|---|
| Cases | Controls | Cases | Controls | OR | 95% CI | P homc | EOR (P) | P homd | |
| All patients | 30 | 83 | 56 | 91 | 3.5 | 1.5–8.6 | NA | 0.27 (<0.001) | NA |
|
Age at testicular cancer diagnosis (years) | |||||||||
| 18–29 | 6 | 21 | 11 | 12 | Inf | 3.5–Inf | 0.56 (0.005) | ||
| 30–39 | 12 | 28 | 21 | 41 | 1.8 | 0.4–7.4 | 0.47 (0.010) | ||
| 40–71 | 12 | 34 | 24 | 38 | 3.3 | 0.9–11.4 | 0.100 | 0.086 (0.062) | >0.5 |
|
Year of testicular cancer diagnosis | |||||||||
| 1959–1969 | 11 | 26 | 13 | 21 | 2.3 | 0.6–9.4 | 0.17 (0.084) | ||
| 1970–1979 | 10 | 33 | 32 | 53 | 7.1 | 1.4–37.6 | 0.50 (<0.001) | ||
| 1980–1987 | 9 | 24 | 11 | 17 | 2.8 | 0.5–15.0 | >0.5 | 0.10 (0.234) | >0.5 |
|
Testicular cancer histology | |||||||||
| Non-seminoma | 11 | 33 | 19 | 23 | 6.2 | 1.6–23.6 | 1.15 (<0.001) | ||
| Seminoma | 19 | 49 | 37 | 68 | 2.8 | 1.1–7.6 | 0.268 | 0.16 (0.013) | 0.210 |
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Age at stomach cancer diagnosis (years) | |||||||||
| 31–49 | 9 | 29 | 15 | 18 | Inf | 4.4–Inf | 0.22 (0.014) | ||
| 50–59 | 10 | 21 | 19 | 34 | 2.4 | 0.5–12.9 | Inf (0.033) | ||
| 60–80 | 11 | 33 | 22 | 39 | 2.4 | 0.7–7.7 | 0.076 | 0.24 (0.013) | >0.5 |
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Year of stomach cancer diagnosis | |||||||||
| 1975–1984 | 7 | 21 | 11 | 13 | 8.3 | 1.0–69.9 | 0.072 (0.081) | ||
| 1985–1994 | 8 | 25 | 25 | 44 | 5.2 | 0.9–29.6 | Inf (0.001) | ||
| 1995–2004 | 15 | 37 | 20 | 34 | 2.0 | 0.6–6.7 | 0.417 | 0.54 (0.007) | 0.136 |
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Stomach cancer site | |||||||||
| Proximal | 7 | 20 | 14 | 20 | 2.2 | 0.6–7.9 | 0.012 (>0.5) | ||
| Bodye | 19 | 32 | 7 | 15 | 0.5 | 0.03–8.0 | 1.48 (0.003) | ||
| Distal | 3 | 28 | 35 | 56 | Inf | 7.1–Inf | 0.012 | Inf (<0.001) | 0.014 |
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Interval from testicular cancer to stomach cancer (years) | |||||||||
| 7–14 | 12 | 33 | 21 | 35 | 2.8 | 0.8–9.8 | 0.096 (0.042) | ||
| 15–19 | 6 | 21 | 15 | 22 | Inf | 3.0–Inf | 0.11 (0.115) | ||
| 20–39 | 12 | 29 | 20 | 34 | 2.3 | 0.6–8.9 | 0.144 | Inf (<0.001) | 0.090 |
Abbreviations: CI=confidence interval; EOR=excess odds ratio; Gy=gray; hom=homogeneity; Inf=infinity; NA=not applicable; OR=odds ratio; Ref=reference; RT=radiotherapy.
For each characteristic of cancer diagnosis, analyses were limited to patients with nonmissing values for this variable. Missing radiation dose was accounted for by an indicator variable. Numbers of missing values are specified in Tables 1 and 2.
For specified matching variables, controls were assigned according to the value for the corresponding case. For example, if the case was 30 years of age at testicular cancer diagnosis and the controls were 29 and 32 years, all the controls would be included in the 30–39-year category in order to keep each full case–control set in the same category.
P-value for test of homogeneity of ORs across categories. Additional analyses of interaction between binary radiation dose (<25 Gy vs ⩾25 Gy) and continuous mean-centred age at or year of diagnosis revealed that the radiation dose effect decreased by 2.4% per year for age at testicular cancer diagnosis (P=0.49), by 0% per year for year of testicular cancer diagnosis (P>0.5), by 5.6% per year for age at stomach cancer diagnosis (P=0.201), by 5.7% per year for year of stomach cancer diagnosis (P=0.353) and by 7.8% per year for latency (P=0.236).
P-value for test of homogeneity of EORs across categories.
Body includes lesser and greater curvature.