Table 2.
Cox proportional hazards analysis of risk factors for development of nonsynchronous second primary malignancy (NSPM) in differentiated thyroid carcinoma
| Covariate | Relative risk | 95% Confidence interval | p-Value |
|---|---|---|---|
| Age at DTC diagnosis by groups (years) | |||
| <50 | 1 | ||
| ≥50 | 2.345 | 1.327–4.144 | 0.003 |
| Period of DTC diagnosis | |||
| Before 1980 | 1 | ||
| 1980–1999 | 1.301 | 0.705–2.398 | 0.400 |
| After 2000 | 1.720 | 0.685–4.317 | 0.248 |
| Stage of DTC by TNM | |||
| Stage I/II | 1 | ||
| Stage III/IV | 1.575 | 0.878–2.827 | 0.128 |
| Cumulative RAI activity (GBq) | |||
| <2.9 | 1 | ||
| 3–8.9 | 2.383 | 1.039–5.256 | 0.040 |
| ≥9.0 | 2.062 | 0.496–8.174 | 0.328 |
| External local radiotherapy | |||
| No | 1 | ||
| Yes | 1.947 | 1.030–3.681 | 0.041 |
DTC differentiated thyroid carcinoma, RAI radioactive iodine or 131I, TNM 6th edition AJCC/UICC tumor–node–metastasis staging system
Bold values mean P < 0.05