114 / 220
the American Joint Cancer Committee/Union
Internationale Contre le Cancer tumor-node-
metastasis staging system, 6th edition classification
already incorporated tumor size. The following var-
iables were entered in the final model: age groups,
sex, period of DTC diagnosis, cumulative RAI activ-
ity, and stage of DTC. Variables that were signifi-
cantly associated with an increased risk of NSPM
were cumulative RAI activity equaled from 3.0 to
8.9 GBq (RR, 2.777; 95% CI, 1.079–7.145;
P
=
.034). Cumulative RAI activity of
>
9.0 GBq was
not significantly associated with risk of NSPM
(RR, 3.149; 95% CI, 0.645–12.816;
P
= .131).
In this cohort, the total person-years of observa-
tion at risk were 10,414. After a median follow-up of
93.5 months (range, 23.4–570.8), 62 (6.9%) pa-
tients developed 1 NSPM and 2 (0.2%) patients
developed 2 NSPMs (ie, 2 separate primary
malignancies
>
12 months after DTC). Overall, 64
patients with NSPM were observed (15 males and 49
females). The median latency period from DTC to
NSPM was 189.5 months (range, 22.8–531.1). A
total of 15 of 64 (23.4%) patients developed NSPM
in the 5 years of follow-up. The median (range) age
of NSPM was 65.6 (23.0–95.5) years old. None had
known hereditary or familial cancer syndromes. In
males, the 3 most common types/sites for NSPM (in
descending order of frequency) were colon (
n
= 3),
prostate (
n
= 3), and liver (
n
= 2). In females, the 3
commonest types or sites of NSPM (in descending
order of frequency) were breast (
n
= 13), colon (
n
= 7), and uterus (
n
= 4).
Table IV
shows the observed
and expected number of cases and SIRs of NSPM in
the RAI
+
and RAI groups for males, females, and
both sexes. When compared to the incidence rate
in the general population, after adjusting for age
Table II.
A bivariable comparison of demographics, type of second primary malignancies, histology of
thyroid carcinoma, and TNM stages between those who did and did not receive radioiodine ablation
RAI
+
group (
n
= 643)
RAI group (
n
= 252)
P
value
*
Median age of DTC diagnosis
47.5 (19.3–88.8)
44.0 (7.1–90.6)
<
.001
Age of DTC by groups, y
.002
<
30
118 (18.4)
66 (26.2)
30–49
280 (43.5)
118 (46.8)
$
50
245 (38.1)
68 (27.0)
Sex (male/female)
133/510
41/211
.133
Period of DTC diagnosis
<
.001
Before 1980
72 (11.2)
42 (16.7)
1980–1999
271 (42.1)
77 (30.6)
After 2000
300 (46.7)
133 (52.8)
Tumor size of DTC, cm
3.0 (0.1–11.0)
2.0 (0.1–7.0)
<
.001
Histological type of DTC
.111
Papillary
505 (78.5)
190 (75.6)
Follicular
138 (21.5)
62 (24.6)
Stage of DTC by TNM
<
.001
I
377 (58.6)
209 (82.9)
II
45 (7.0)
14 (5.6)
III
121 (18.8)
15 (6.0)
IV
100 (15.6)
14 (5.6)
Type/site of NSPM
y
All sites
56 (8.7)
8 (3.2)
.004
Breast
13 (2.0)
2 (0.8)
.120
Colon
9 (1.4)
1 (0.4)
.468
Lung
4 (0.6)
1 (0.4)
1.000
Liver
3 (0.5)
1 (0.4)
1.000
Corpus uteri
3 (0.5)
1 (0.4)
1.000
Stomach
3 (0.5)
0 (0.0)
.567
Non-Hodgkin lymphoma
3 (0.5)
0 (0.0)
.567
Rectum
2 (0.3)
1 (0.4)
1.000
Cervix
2 (0.3)
1 (0.4)
1.000
*
P
values were generated by using bivariable tests including
v
2
, Fisher exact, and Mann–Whitney
U
tests wherever appropriate.
y
Only nonsynchronous second primary malignancy with a total number
$
3 was listed.
DTC
, Differentiated thyroid carcinoma;
NSPM
, nonsynchronous second primary malignancy;
TNM
, American Joint Cancer Committee/Union Interna-
tionale Contre le Cancer tumor-nodes-metastasis staging system, 6th edition.
Surgery
Volume 151, Number 6
Lang
et
al
94