Models for Site-Specific Solid Cancers Other Than Breast and Thyroid

Although the committee provides risk estimates for both cancer incidence and mortality, models for site-specific cancers were based on cancer incidence data. This was done primarily because site-specific cancer incidence data are based on diagnostic information that is more detailed and accurate than death certificate data and because, for several sites, the number of incident cases is considerably larger than the number of deaths (see annex Table 12B-2). However, models developed from incidence data were checked for consistency with mortality data. Since there is little evidence that radiation-induced cancers are more rapidly fatal than cancer that occurs for other reasons, ERR models based on incidence data can be used directly to estimate risks of cancer mortality, whereas EAR models require adjustment. (See “Method of Calculating Lifetime Risks” for a description of how the models are used to estimate risks of cancer incidence and mortality.)

Models for estimating risks of solid cancers of specific sites other than breast and thyroid were also of the form shown in Equation (12-2). The committee’s approach to quantifying the parameters γ and η was to use the estimates obtained from analyzing incidence data on all solid cancers excluding thyroid and nonmelanoma skin cancers (shown in Table 12-1) unless site-specific analyses indicated significant departure from these estimates. This approach is similar to that used by UNSCEAR (2000b) except that the committee estimated the parameters βM and βF separately for each site of interest.

The committee’s preferred ERR and EAR models for site-specific cancer incidence and mortality are shown in Table 12-2. The estimates of βM and βF are for a person exposed at age 30 or older at an attained age of 60. Models for breast and thyroid cancer were based on published analyses that included data on medically exposed persons as discussed in the next two sections. For other sites, common values of the parameter γ indicating dependence on age at exposure could be used in all cases. With the ERR models, common values of the parameter indicating the dependence of risks on attained age (η) could be used in all cases except the category “all other solid cancers.” With the EAR models, it was necessary to estimate the attained-age parameter, η, separately for cancers of the liver, lung, and bladder, which may reflect variation in the pattern of increase with age for site-specific baseline rates.

The committee emphasizes that there is considerable uncertainty in models for site-specific cancers. Statistical uncertainty in the estimates of the main effect parameter βs is

 

TABLE 12-2 Committee’s Preferred ERR and EAR Models for Estimating Site-Specific Solid Cancer Incidence and Mortalitya

Cancer Site

No. of Cases

ERR Models

EAR Models

βMb (95% CI)

βFb (95% CI)

γc

ηd

βMe (95% CI)

βFe (95% CI)

γc

ηd

Stomach

3602

0.21 (0.11, 0.40)

0.48 (0.31, 0.73)

−0.30

−1.4

4.9 (2.7, 8.9)

4.9 (3.2, 7.3)

−0.41

2.8

Colon

1165

0.63 (0.37, 1.1)

0.43 (0.19, 0.96)

−0.30

−1.4

3.2 (1.8, 5.6)

1.6 (0.8, 3.2)

−0.41

2.8

Liver

1146

0.32 (0.16, 0.64)

0.32 (0.10, 1.0)

−0.30

−1.4

2.2 (1.9, 5.3)

1.0 (0.4, 2.5)

−0.41

4.1 (1.9, 6.4)

Lung

1344

0.32 (0.15, 0.70)

1.40 (0.94, 2.1)

−0.30

−1.4

2.3 (1.1, 5.0)

3.4 (2.3, 4.9)

−0.41

5.2 (3.8, 6.6)

Breast

952

0.51 (0.28, 0.83)

0

−2.0

9.9f (7.1, 14)

−0.51

3.5, 1.1g

Prostate

281

0.12 (<0, 0.69)

−0.30

−1.4

0.11 (<0, 1.0)

−0.41

2.8

Uterus

875

0.055 (<0, 0.22)

−0.30

−1.4

1.2 (< 0, 2.6)

−0.41

2.8

Ovary

190

0.38 (0.10, 1.4)

−0.30

−1.4

0.70 (0.2, 2.1)

−0.41

2.8

Bladder

352

0.50 (0.18, 1.4)

1.65 (0.69, 4.0)

−0.30

−1.4

1.2 (0.4, 3.7)

0.75 (0.3, 1.7)

−0.41

6.0 (3.1, 9.0)

Other solid cancers

2969

0.27 (0.15, 0.50)

0.45 (0.27, 0.75)

−0.30

−2.8 (−4.1, −1.5)

6.2 (3.8, 10.0)

4.8 (3.2, 7.3)

−0.41

2.8

Thyroidh

 

0.53 (0.14, 2.0)

1.05 (0.28, 3.9)

−0.83

0

 

NOTE: Estimated parameters with 95% CIs. PY = person-years.

aThe ERR or EAR is of the form βsD exp (γ e*) (a / 60)η, where D is the dose (Sv), e is age at exposure (years), e* is (e − 30) / 10 for e < 30 and zero for e 30, and a is attained age (years). Models for breast and thyroid cancer are based on e instead of e*, although γ is still expressed per decade.

bERR/Sv for exposure at age 30+ at attained age 60.

cPer-decade increase in age at exposure over the range 0–30 years (γ).

dExponent of attained age (η).

eEAR per 104 PY-Sv for exposure at age 30+ and attained age 60; these values are for cancer incidence and must be adjusted as described in the text to estimate cancer mortality risks.

fBased on a pooled analysis by Preston and others (2002a). See text for details. Unlike other EAR (βF) shown in this table, the estimate of 9.9 is for exposure at age 25 and attained age 50. The ERR estimate of 0.51, however, is for an attained age of 60 and applies to all exposure ages since γ=0.

gThe first number is for attained ages less than 50; the second number is for attained ages 50 or greater.

hBased on a pooled analyses by Ron and others (1995a) and NIH (2003). Confidence intervals are based on standard errors of non-sex-specific estimates with allowance for heterogeneity among studies.



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