Table 2. Multivariate Analysis of Breast Cancer-Specific Mortality (BCSM).

Variable	BCSM		Pairwise*
	HR [95% CI]	P1 value	HR [95% CI]	P2 value
Age of Diagnosis
20–39	1.000 [Reference]
40–59	0.784 [0.752–0.818]	<.0001
60–79	0.964 [0.924–1.007]	.098
Year of Diagnosis
1990–1994	1.000 [Reference]
1995–1999	0.817 [0.788–0.847]	<.0001
2000–2004	0.681 [0.657–0.705]	<.0001
2005–2009	0.570 [0.545–0.597]	<.0001
Tumor Size
0–2 cm	1.000 [Reference]
2–5 cm	2.286 [2.223–2.350]	<.0001
>5 cm	3.714 [3.551–3.885]	<.0001
LN Status
Negative	1.000 [Reference]
Positive	2,811 [2.736–2.888]	<.0001
ER Status
Negative	1.000 [Reference]
Positive	0.623 [0.601–0.645]	<.0001
PR Status
Negative	1.000 [Reference]
Positive	0.716 [0.691–0.741]	<.0001
Radiotherapy
Without RT	1.000 [Reference]
With RT	0.892 [0.870–0.915]	<.0001
Laterality
Left-sided	1.000 [Reference]
Right-sided	0.988 [0.964–1.013]	.331
Primary Site		<.0001
UO	1.000 [Reference]		0.920 [0.880–0.961	<.0001
UI	1.242 [1.199–1.287]	<.0001	1.142 [1.085–1.203]	<.0001
LI	1.329 [1.270–1.391]	<.0001	1.222 [1.152–1.296]	<.0001
LO	1.137 [1.091–1.185]	<.0001	1.046 [0.989–1.105]	.117
CEN	1.087 [1.041–1.136]	<.0001	1.000 [Reference]

Abbreviations: HR =  hazard ratio; CI =  confidence interval; AJCC =  American Joint Committee on Cancer; LN =  lymph node; ER =  estrogen receptor; PR =  progesterone receptor; RT =  radiotherapy; UO =  upper outer quadrant of breast; UI =  upper inner quadrant of breast; LI =  lower inner quadrant of breast; LO =  lower outer quadrant of breast; CEN =  central portion quadrant of breast.

*Pairwise comparisons were conducted to clarify the difference on HR at different primary site. P₁ value, using UO as the reference, indicated best prognosis for patients with tumors at UO. From another point of view, P₂ value, using CEN as the reference, indicated that patients with tumors at CEN and LO had worse prognosis than those at UO, but better prognosis than those at UI and LI.