Survival Implications Associated with Variation in Mastectomy Rates for Early-Staged Breast Cancer
Table 1
Early-stage breast cancer patient characteristics by surgery choice and instrumental variable-based patient quintile groups.
Covariates
Surgery choice
Instrument quintile groups (higher area treatment ratio (ATR)→)
Variable
Category
Total
BCSR
Mastectomy
value
1
2
3
4
5
value
Column %
Column %
Surgery
Mastectomy
16,103 (56%)
0
100%
na
37.9
50.2
59.7
65.7
68.6
<0.0001*
BCSR
12,572 (44%)
100%
0%
62.1
49.8
40.3
34.3
31.4
<0.0001*
Age
66–75
16,442 (57%)
63.9
52.2
<0.0001*
57.8
58.0
56.2
57.4
57.3
0.2251
76+
12,233 (43%)
36.1
47.8
42.2
42.0
43.8
42.6
42.7
0.2251
Stage at diagnosis
Stage I
17,908 (62%)
75.1
52.6
<0.0001*
63.8
62.0
62.4
60.8
63.2
0.0908
Stage IIa
7,700 (27%)
20.1
32.1
25.7
27.5
26.7
27.8
26.6
0.1261
Stage IIb
2,827 (10%)
4.4
14.1
9.7
9.6
10.1
10.6
9.3
0.4096
Stage IInos
240 (1%)
0.4
1.2
0.8
0.9
0.8
0.8
0.9
0.2169
Tumor size
10
8,797 (31%)
40
23.4
<0.0001*
31.3
30.3
30.0
29.9
31.9
0.3633
11–20
11,958 (42%)
43.4
40.3
42.1
41.8
42.5
40.8
41.4
0.1152
>21
7,680 (27%)
16.2
35.1
25.8
27.1
26.7
28.5
25.8
0.2090
unknown
240 (1%)
0.4
1.2
0.8
0.9
0.8
0.8
0.9
0.2169
Grade
Well differentiated
4,751 (17%)
20.7
13.4
<0.0001*
16.4
17.0
16.0
16.1
17.4
0.2426
Moderately differentiated
10,804 (38%)
39.9
35.9
39.3
38.4
37.3
36.6
36.6
0.0002*
Poorly differentiated
6,718 (23%)
20.3
25.9
23.1
22.4
24.4
24.6
22.6
0.2138
Undifferentiated/unknown
6,402 (22%)
19.1
24.9
21.2
22.1
22.3
22.7
23.3
0.0031*
Comorbidity
Below median
15,784 (55%)
58.1
52.7
<0.0001*
54.6
55.7
54.7
56.0
54.1
0.3759
Above median
12,891 (45%)
41.9
47.3
45.4
44.3
45.3
44.0
45.9
0.3759
Physician surgical volume
Low volume
8,510 (30%)
26.0
32.6
<0.0001*
27.5
33.2
30.3
29.2
28.4
0.1447
High volume
20,165 (70%)
74.0
67.4
72.5
66.8
69.7
70.9
71.6
0.1447
Hospital bed size
350
15,461 (54%)
52.6
54.9
<0.0001*
54.8
57.7
56.8
52.1
47.9
<0.0001*
351+
13,214 (46%)
47.4
45.1
45.2
42.3
43.2
47.9
52.1
<0.0001*
Residence area size
Metro
24,530 (86%)
90.7
81.5
<0.0001*
91.0
87.8
78.8
77.4
92.7
<0.0001*
Nonmetro
4,145 (14%)
9.3
18.5
9.0
12.2
21.2
22.6
7.3
<0.0001*
Area median income
Above median
14,483 (51%)
53.9
47.8
<0.0001*
52.4
51.9
41.8
50.2
56.3
0.0032*
Below median
13,730 (48%)
44.6
50.4
46.9
46.3
57.3
46.6
42.2
0.0001*
Missing
462 (2%)
1.5
1.7
0.7
1.8
0.9
3.2
1.5
<0.0001*
aTest of difference in characteristic distribution between surgery choices.
bCochran-Armitage test of trend in characteristic value across patients grouped into quintiles based on local area mastectomy practice style measure. For example, the value for stage I tests whether a linear trend in stage I diagnoses exists across the instrument-based patient groups.
*.
