Table 2.

Factors associated with the development of brain metastases

		Univariate analysis			Multivariate analysis
		Incidence of BM (%)
Factors	1-yr	3-yr	5-yr	P	P	RR (95 % CI)
Gender
Male	7.6	20.5	26.9	0.012
Female	13.3	33.4	43.0
Age
≤60 yrs	14.1	28.8	37.9	0.035
>60 yrs	3.9	19.3	24.9
Smoking History
Negative	11.7	28.6	37.9	0.038
Positive	7.2	21.0	26.8
Histology
Non- squamous cell cancer	12.0	34.6	44.3	0.000	0.001	4.13(1.86-9.19)
Squamous cell cancer	5.0	8.3	11.4
Tumor stage
T1	5.9	20.1	36.1	0.596
T2	8.3	22.6	30.1
T3	14.4	36.9	36.9
Laterality
Left	9.8	26.8	33.9	0.456
Right	8.7	22.2	30.3
Location
Upper/middle lobe	7.8	22.3	31.7	0.798
Lower lobe	11.5	27.2	31.6
Histologic grade
Well/moderate	8.8	21.7	31.1	0.601
Poor	11.4	29.5	33.0
Adjuvant chemotherapy
No	11.0	21.2	24.7	0.511
Yes	8.5	25.1	33.8
Postoperative radiotherapy
No	9.5	25.3	34.4	0.344
Yes	8.7	23.0	29.0
No. of metastatic lymphonodes
≤5	4.6	13.3	20.9	0.000
>5	14.5	38.6	46.3
LNR
≥ 30 %	15.3	39.2	46.4	0.000	0.000	3.33(1.79-6.18)
< 30 %	2.9	10.3	18.4
No. of metastatic mediastinal lymphonodes
< 3	4.9	13.8	21.0	0.001
≥ 3	13.6	35.2	43.0
No. of metastatic mediastinal lymphonodes station
1	6.0	14.8	21.8	0.000
2-4	15.1	42.7	51.6
Ratio of metastatic mediastinal lymphonodes station
≤50 %	3.8	13.8	19.5	0.000
>50 %	15.0	35.8	44.9

BM indicates brain metastases; RR, relative risk; LNR, lymph node ratio.