Table 5. Biological markers, 2013 (KBCS registry data).

Biologic marker	No. of patients (%)
ER
Negative	2,557 (24.5)
Positive	7,828 (74.9)
Unknown	64 (0.6)
Total	10,449 (100.0)
PR
Negative	3,624 (34.8)
Positive	6,739 (64.6)
Unknown	65 (0.6)
Total	10,428 (100.0)
c-erbB-2
Negative	3,351 (32.7)
Weak (1+)	2,602 (25.4)
Intermediate (2+)	2,046 (19.9)
Strong (3+)	1,864 (18.2)
Unknown	394 (3.8)
Total	10,257 (100.0)

KBCS=Korean Breast Cancer Society; ER=estrogen receptor; PR=progesterone receptor.