Table 4. Measures for estimation of synergic effect between histology subtype and N stage for the risk of distant metastasis in DTC.

Histology subtype	N stage	M1 case (%)	Total case	Odds ratio (95% CI)	P value
PTC	0	371 (0.5)	69,343	Reference
	1	684 (3.3)	20,750	3.801 (3.224–4.482)	<0.001*
FTC	0	188 (3.5)	5,350	5.685 (4.576–7.062)	<0.001*
	1	69 (32.4)	213	33.495 (22.402–50.083)	<0.001*
RERI	76.973 (50.238–103.708)
AP	0.864 (0.823–0.905)
SI	7.930 (5.833–10.780)

Adjusted for age at diagnosis, sex, race, tumor size, extrathyroidal extension. *, represent the P value <0.05. DTC, differentiated thyroid cancer; PTC, papillary thyroid cancer; CI, confidence interval; FTC, follicular thyroid cancer; RERI, relative excess risk; AP, attributable proportion; SI, synergy index.