Association between unilateral or bilateral mastectomy and breast cancer death in patients with unilateral ductal carcinoma

Figures & data

Table 1 Pre-match patient characteristics

Characteristics	N	Bilateral % (n)	Unilateral % (n)	Test statistic
		N = 2,815	N = 38,695
Year of diagnosis	41,510			${\chi }_4^2=150.74$, p < 0.001
1998		7 (204)	12 (4,808)
1999		9 (261)	12 (4,686)
2000		22 (630)	25 (9,753)
2001		30 (834)	26 (9,975)
2002		31 (886)	24 (9,473)
Stage	41,510			${\chi }_3^2=104.39$, p < 0.001
I		43 (1197)	35 (13,386)
IIA		27 (752)	26 (10,119)
IIB		12 (330)	14 (5,566)
IIIA		10 (293)	12 (4,782)
IIIB		2 (67)	3 (1,273)
IIIC		5 (132)	6 (2,400)
IIINOS		0 (9)	1 (206)
IV		1 (35)	2 (959)
Age at diagnosis (y)	41,510	51 (43,59)	49 (59,72)	F1.41509 = 840.69, p < 0.001
Race				${\chi }_3^2=158.88$, p < 0.001
White	41,510	90 (2,532)	80 (31,079)
Black		5 (146)	10 (3,896)
Other		5 (131)	9 (3,626)
Unknown		0 (6)	0 (94)
Node involvement				${\chi }_2^2=59.82$, p < 0.001
0 nodes	41,510	56 (1,566)	50 (19,367)
1–3 nodes		27 (771)	27 (10,389)
>3 nodes		17 (478)	23 (8,939)
Tumor size (mm)	40,607	10 (17,28)	13 (20,32)	F1.40605 =163.43, p < 0.001
Tumor size	41,510			${\chi }_3^2=134.53$, p < 0.001
0–20 mm		53 (1,499)	43 (16,528)
21–40 mm		32 (894)	36 (14,083)
41+ mm		13 (358)	19 (7,245)
Unknown		2 (64)	2 (839)
Grade	41,510			${\chi }_4^2=15.11$, p = 0.004
I		13 (375)	12 (4,522)
II		37 (1,037)	38 (14,755)
III		43 (1,211)	44 (17,158)
IV		3 (83)	2 (850)
Unknown		4 (109)	4 (1,410)
Reconstruction (yes)	41,510	39 (1,104)	13 (5,052)	${\chi }_1^2=1422.03$, p < 0.001
Receptor status
ER: positive	41,510	61 (1,722)	61 (23,515)	${\chi }_3^2=6.14$, p = 0.105
ER: negative		25 (696)	24 (9,096)
ER: borderline		0 (6)	0 (89)
ER: unknown		14 (391)	15 (5,995)
PR: positive		53 (1,482)	50 (19,429)	${\chi }_3^2=13.61.$ p = 0.003
PR: negative		32 (907)	32 (12,404)
PR: borderline		0 (11)	1 (217)
PR: unknown		15 (415)	17 (6,645)

Abbreviations: ER, estrogen receptor; PR, progesterone receptor.

Table 2 Post-match patient characteristics

	N	Bilateral % (n)	Unilateral % (n)	Test statistic
		N = 2,815	N = 11,260
Year of diagnosis	14,075			${\chi }_4^2=0$, p = 1
1998		7 (204)	7 (816)
1999		9 (261)	9 (1,044)
2000		22 (630)	22 (2,520)
2001		30 (834)	30 (3,336)
2002		31 (886)	31 (3,544)
Stage	14,075			${\chi }_4^2=0$, p = 1
I		43 (1,197)	43 (4,788)
IIA		27 (752)	27 (3,008)
IIB		12 (330)	12 (1,320)
III		18 (501)	18 (2,004)
IV		1 (35)	1 (140)
Age at diagnosis (y)	14,075	43 (51,59)	43 (51,59)	F1.14073 = 0.16, p = 0.689
Race	14,075			${\chi }_3^2=133.86$, p < 0.001
White		90 (2,532)	81 (9,112)
Black		5 (146)	12 (1,295)
Other		5 (131)	7 (827)
Unknown		0 (6)	0 (26)
Node involvement	14,075			${\chi }_2^2=9.59$, p = 0.008
0 nodes		56 (1,566)	57 (6,445)
1–3 nodes		27 (771)	25 (2,772)
>3 nodes		17 (478)	18 (2,043)
Tumor size (mm)	13,788	10 (17,28)	12 (19,30)	F1.13786 = 14.02, p < 0.001
Tumor size	9,446			${\chi }_2^2=8.55$, p < 0.014
0–20 mm		78 (1,499)	75 (5,675)
21–40 mm		0 (0)	0 (0)
41+ mm		19 (358)	22 (1,627)
Unknown		3 (64)	3 (223)
Grade	14,075			${\chi }_4^2=30.19$, p < 0.001
I		13 (375)	11 (1,238)
II		37 (1,037)	37 (4,122)
III		43 (1,211)	47 (5,256)
IV		3 (83)	2 (209)
Unknown		4 (109)	4 (435)
Reconstruction (yes)	14,075	39 (1,104)	21 (2,318)	${\chi }_1^2=424.86$, p < 0.001
Receptor status	14,075
ER: positive		61 (1,722)	60 (6,734)	${\chi }_1^2=424.86$, p < 0.001
ER: negative		25 (696)	26 (2,909)
ER: borderline		0 (6)	0 (27)
ER: unknown		14 (391)	14 (1,590)
PR: positive		53 (1,482)	51 (5,724)	${\chi }_3^2=1.94$4, p = 0.585
PR: negative		32 (907)	34 (3,789)
PR: borderline		0 (11)	1 (62)
PR: unknown		15 (415)	15 (1,685)

Abbreviations: ER, estrogen receptor; PR, progesterone receptor.

Figure 1 Kaplan–Meier survival curves comparing breast cancer–specific survival of patients who underwent unilateral mastectomy or bilateral mastectomy for unilateral breast cancer.

Table 3 Cox proportional hazards model with adjustment for matching and additional covariates

Variables	Category	Hazard ratio and 95% confidence limits	p-value
Mastectomy	Bilateral vs unilateral	0.92 (0.83, 1.02)	0.109
Race	Black vs white	1.5 (1.35, 1.67)	<0.0001
	Other vs white	0.97 (0.83, 1.15)	0.7512
	Unknown vs white	0.2 (0.03, 1.37)	0.101
Radiation	Radiation vs no radiation	0.93 (0.85, 1.02)	0.1134
Reconstruction	Reconstruction vs no reconstruction	0.87 (0.79, 0.96)	0.0074
Receptor status (ER)	Borderline vs negative	0.47 (0.17, 1.28)	0.1398
	Positive vs negative	0.76 (0.67, 0.85)	<0.0001
	Unknown vs negative	0.88 (0.6, 1.3)	0.5221
Receptor status (PR)	Borderline vs negative	1.18 (0.69, 2.02)	0.5399
	Positive vs negative	0.71 (0.64, 0.8)	<0.0001
	Unknown vs negative	0.82 (0.56, 1.19)	0.2898

Abbreviations: ER, estrogen receptor; PR, progesterone receptor.