2017 Section 7 Green Book

calculated by dividing observed incidence rates in

our cohort by expected incidence rates in the gen-

eral population. The observed number of each

NSPM was calculated by compiling the person-

years of observation according to 5-year age groups

by sex from the diagnosis of DTC to the date of

death, date of last follow-up, or date of diagnosis

of NSPM, whichever occurred first. The expected

number of each NSPM in 5-year age groups by

sex were derived from cancer incidence statistics

in 2008 reported by the Hong Kong Cancer Regis-

try

( http://www3.ha.org.hk/cancereg/ )

and were

multiplied by the accumulated person-years of ob-

servation at risk to obtain the expected number of

NSPM.

For the comparison for dichotomous variables

between the RAI

and RAI groups,

and Fisher

exact tests were used. The Mann–Whitney

test

was used for the comparison of continuous varia-

bles between RAI

and RAI groups. All statistical

analyses were conducted using SPSS software (ver-

sion 18.0; SPSS, Inc., Chicago, IL).

RESULTS

Table I

shows the baseline patient characteris-

tics. Six hundred ninety-five (77.7%) patients had

papillary thyroid carcinoma and 200 (22.3%) had

follicular thyroid carcinoma. The majority were fe-

male (80.6%) and ethnic Chinese (94.1%). The

median age of DTC diagnosis was 44.0 years

(range, 7.1–90.6), and the median follow-up pe-

riod was 93.5 months (range, 23.1–570.8). Seven

hundred sixty-three (85.3%) patients underwent

bilateral thyroid resection, and of these, 643

(84.3%) patients received at least 1 course of RAI

therapy, whereas of the 132 (14.7%) patients who

underwent unilateral thyroid resection, no patient

received RAI therapy. There were 55 (6.1%) pa-

tients who received

2 doses of RAI therapy.

Table II

shows a comparison of demographics, pe-

riod of DTC diagnosis, number and type of NSPM,

major histologic types of DTC, and stage of DTC

between the RAI

and RAI groups. Patients in

the RAI

group were significantly older at the

time of DTC diagnosis (47.5 vs 44.0;

.001)

and there was a significantly greater proportion

of patients belonging to the

50-year-old age

group (39.9% vs 28.2%;

.001). There were a

similar proportion of males in the 2 groups.

When the periods of DTC diagnosis were com-

pared, there were a significantly greater propor-

tion of patients not receiving RAI treatment

towards the later period. Tumor size was signifi-

cantly larger in the RAI

group because size was

an important criterion for RAI ablation. Similarly,

the stages of DTC were more advanced in the

RAI

group as reflected by the higher proportion

of stage III and IV patients (18.8% vs 6.0% and

15.6% vs 5.6%, respectively;

.001). In terms

of the type of NSPM, primary breast, colon, and

lung cancers were the 3 most common NSPMs in

the RAI

and RAI groups.

The

Figure

shows the cumulative risk of devel-

oping NSPM after the diagnosis of DTC in the

RAI

and RAI groups. The 20-year cumulative

risk of NSPM in the RAI

group was significantly

higher than that in the RAI group (13.5% vs

3.1%;

= .015). The mean times to development

of NSPM in the RAI

and RAI groups were

34.37 years (95% CI, 32.6–36.1) and 43.05 years

(95% CI, 40.3–45.8).

Table III

shows the Cox proportional hazards

analysis of factors influencing the development of

NSPM in patients with DTC. The analysis included

variables that were significant in the comparison

between RAI

and RAI groups and factors that

might be linked to development of NSPM. Tumor

size was not entered because the stages of DTC by

Table I.

Baseline patient demographics and char-

acteristics (

= 895)

Median Range or %

Age at diagnosis of DTC, y

44.0 7.1–90.6

Sex

Male

174

19.4

Female

721

80.6

Major histologic types of DTC

Papillary

695

77.7

Follicular

200

22.3

Tumor stage of DTC by TNM

586

65.5

6.6

III

136

15.2

114

12.7

Follow-up time, months

93.5 23.4–570.8

No. of patients with NSPM

detected during follow-up

7.2

Latency period to NSPM

from time of DTC, months

189.5 22.8–531.1

Radiation exposure

No RAI therapy given

252

28.2

RAI therapy given

643

71.8

1 course

588

65.7

2 courses

2.9

3 courses

3.2

*Only second primary malignancy which occurred

12 months after the

diagnosis of DTC was included.

DTC

, Differentiated thyroid carcinoma;

NSPM

, nonsynchronous second

primary malignancy;

RAI

, radioactive iodine;

TNM

, American Joint Can-

cer Committee/Union Internationale Contre le Cancer tumor-nodes-

metastasis staging system, 6th edition.

Surgery

June 2012

Lang