Table 2.
Risk of pancreatic cancer associated with radiation dose to the site of the pancreatic tumor (matched location for controls) and receipt of alkylating agent (AA)-containing chemotherapy for Hodgkin lymphoma (HL)
| HL treatment | Cases/Controls (N) (36/70) | ORa (95% CI) | P-value |
|---|---|---|---|
| Radiation dose (Gy)b | |||
| 0 to <0.5 | 9/25c | 1.0 | |
| 0.5 to <5d | 6/24 | 0.5 (0.1–2.0) | |
| 10d to <40 | 10/12e | 1.8 (0.5–8.1) | |
| ≥40 | 9/6 | 9.1 (1.7–77) | Ptrend = 0.0050 |
| Unknown | 2/3 | 1.0 (0.1–8.7) | |
| Total | 36/70 | ||
| EOR per Gyf | 0.098 (0.015–0.42) | ||
| Chemotherapy (number of AA cycles)g | |||
| 0 | 10/33 | 1.0 (referent) | |
| 1–5 | 5/9 | 1.0 (0.2–4.4) | |
| 6 | 7/12 | 3.7 (0.9–19) | |
| 7–10 | 6/8 | 3.6 (0.8–18) | |
| >10 | 7/7 | 3.7 (0.9–19) | Ptrend = 0.008 |
| Unknown | 1/1 | 4.9 (0.1–172) | |
| Radiation dose (Gy) and chemotherapy (number of AA cycles)h | |||
| <10 and <6 | 9/28 | 1.0 | |
| ≥10 and <6 | 6/12 | 3.0 (0.7–17) | |
| <10 and ≥6 | 6/20 | 1.8 (0.4–9.7) | |
| ≥10 and ≥6 | 13/6 | 17.9 (3.5–158) | Pmultiplicative interaction = 0.29 |
| Padditive interaction = 0.041 | |||
aThe ORs presented differ from crude ORs because they take account of the matching and of the modest positive correlation between radiation dose and number of AA cycles.
bAdjusted for number of AA-containing cycles.
cIncludes 3 cases and 12 controls who did not receive radiotherapy and one control who received radiotherapy only in the period within 5 years of the date of pancreatic cancer diagnosis in the associated case.
dThere were no subjects in the 5 to <10 Gy category.
eIncludes five cases and three controls with doses in the 10 to <30 Gy range and five cases and nine controls in the 30 to <40 Gy range.
fRadiation dose was treated as a continuous variable.
gAdjusted for radiotherapy (continuous linear variable). In order to reduce the influence of outliers, the continuous variable for the number of AA-containing cycles was truncated at 30 cycles. This truncation affected a case with 66 AA cycles and a control with 41 AA cycles.
hOur findings of positive trends with both radiation dose and the number of AA cycles persisted in analyses that excluded one registry at a time except that the trends did not reach statistical significance when Sweden, the registry contributing the largest number of cases, was excluded (P = 0.053 for radiation dose; P = 0.17 for number of AA cycles). Significant positive trends persisted in analyses that excluded either patients for whom radiotherapy data were incomplete (3 cases, 6 controls) or case sets for whom the pancreatic cancer diagnosis was not histologically confirmed (8 cases, 16 controls).
CI, confidence interval; EOR, excess odds ratio; Gy, Gray; OR, odds ratio.