J Korean Neurosurg Soc 52 | September 2012 Table 2. Univariable analysis of factors possibly affecting the cumulative incidence of leptomeningeal seeding after surgical resection or whole brain radiotherapy for brain metastases Variables No. of patients (%)* No LMC (n=156) LMC (n=27) Hazard ratio Cumulative incidence 95% CI p value p value <0.001 Index procedure Surgical resection 17 (11) 10 (37) 2.95 WBRT 139 (89) 17 (63) 1.0 1.33-6.54 0.008 Age 0.006 <40 16 (10) 8 (30) 2.36 ≥40 140 (90) 19 (70) 1.0 0.98-5.65 0.055 Time from diagnosis to brain metastasis 0.893 <12 months 16 (10) 3 (11) 1.18 ≥12 months 140 (90) 24 (89) 1.0 0.35-3.95 0.787 Tumor volume 0.057 ≤4.3 mL3 83 (53) 9 (33) 1.0 >4.3 mL3 73 (47) 18 (67) 1.63 0.72-3.66 0.241 No. of lesions 0.015 Single 44 (28) 14 (52) 1.0 Multiple 112 (72) 13 (48) 0.53 0.24-1.15 0.108 Location 0.045 Supratentorial 40 (25) 12 (44) 1.0 Infratentorial 116 (75) 15 (56) 0.66 0.30-1.42 0.285 Adjuvant chemotherapy 0.449 No 70 (45) 10 (37) 1.0 Yes 86 (55) 17 (63) 0.51 0.23-1.15 0.104 KPS 0.218 ≥70 138 (88) 26 (96) 1.0 <70 18 (12) 1 (4) 0.31 0.04-2.28 0.249 Systemic disease status 0.489 PNrEoDgre&sssitnagble 9597 ((6337)) 189 ((3700)) 21..008 0.87-4.95 0.099 *Numbers in parenthesis represents column percentage. LMC : leptomeningeal carcinomatosis, WBRT : wholebrain radiation therapy, KPS : Karnofsky Performance Status, NED : no evidence of disease, CI : confidence interval pared to the WBRT group, the HR of the SR group was 4.03 (95% CI, 1.51-10.73; p=0.005). The HR of the younger age (<40) group was 2.89 (95% CI, 1.16-7.19; p=0.022), adjuvant chemo- therapy group decreased the risk for development of LMC at a HR of 0.43 (95% CI, 0.19-0.99; p=0.048), whereas patients with progressing systemic disease showed increased risk of LMC at a HR of 3.53 compared with NED or stable systemic disease (95% CI, 1.35-9.23; p=0.010). Differential effects of the index procedure on the incidence of LMS according to the age group To evaluate the differential effect of treatment modality on the development of LMC according to the age group, we performed the subgroup analysis presented in Table 4. For the different modes of treatment, WBRT group showed lower incidence of LMC in the old age (≥40) group (Fisher’s exact test, p=0.005), whereas the difference according to the index procedure be- came not significant in the young age (<40) group due to high incidence of LMC regardless of the index procedures. DISCUSSION Brain metastases increase the risk of LMC in breast cancer? LMC most often presents in patients with progressive systemic cancer. However, occasionally it occurs in the absence of systemic disease, and it can even be the first manifestation of cancer5). Thus, LMC can develop independently from systemic malignan- cy without PBM, but some studies reported that patients who underwent SR for their PBM had a higher incidence of LMC compared with that of patients received non surgical treat- ments31-33). It is unclear how PBM spreads and causes LMC, but we could observe the surgical spillage or the drop-metastasis of malignant brain tumors2,25,35). The incidence of LMC in patients with PBM compared with that in patients without PBM are yet to be studied, and even reports investigating the incidence of LMC in patients with PBM are rare17,18,30). Kim et al.17) reported that in 400 patients with CNS metastases of breast cancer, 318 patients (79.5%) had PBM only, 52 patients (13%) had both PBM and 196