Comparison of the 7th and 8th edition of American Joint Committee on Cancer (AJCC) staging systems for breast cancer patients: a Surveillance, Epidemiology and End Results (SEER) Analysis

Figures & data

Table 1 Baseline characteristics of the included patients (n=168,076)

Characteristics	No.	%
Age at diagnosis (years)
≤39	8,860	5.3
40–49	29,624	17.6
50–59	42,900	25.5
60–69	44,966	26.8
70–79	27,842	16.6
≥80	13,884	8.3
Race/ethnicity
Hispanic	19,006	11.3
NH Black	17,919	10.7
NH White	115,520	68.7
NH Asian or Pacific Islander	14,662	8.7
NH American Indian/Alaska Native	969	0.6
Sex
Male	1,104	0.7
Female	166,972	99.3
Grade
I	42,252	25.1
II	69,759	41.5
III–IV	56,065	33.4
ER status
Positive	137,137	81.6
Negative	30,939	18.4
PR status
Positive	122,002	72.6
Negative	46,074	27.4
HER2 status
Positive	25,446	15.1
Negative	142,630	84.9
ER and PR status
ER and PR positive	120,209	71.5
ER positive, PR negative	16,928	10.1
ER and PR negative	29,146	17.3
ER negative, PR positive	1,793	1.1
ER, PR and HER2 status
ER positive, PR positive, and HER2 positive	12,297	7.3
ER positive, PR positive, and HER2 negative	107,912	64.2
ER positive, PR negative, and HER2 positive	4,707	2.8
ER positive, PR negative, and HER2 negative	12,221	7.3
ER negative, PR positive, and HER2 positive	446	0.3
ER negative, PR positive, and HER2 negative	1,347	0.8
ER negative, PR negative, and HER2 positive	7,996	4.8
ER negative, PR negative, and HER2 negative	21,150	12.6
7th AJCC TNM stage
Stage IA	88,985	52.9
Stage IB	4,567	2.7
Stage IIA	43,124	25.7
Stage IIB	9,562	5.7
Stage IIIA	12,897	7.7
Stage IIIB	3,736	2.2
Stage IIIC	5,205	3.1
Follow-up time (months)
Median	20
Range	0–59

Abbreviations: AJCC, American Joint Committee on Cancer; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; M, distant metastases; N, regional nodes; NH, non-Hispanic; PR, progesterone receptor; T, primary tumor.

Table 2 Comparison of the 7th AJCC staging system and 8th AJCC prognostic staging system (n=168,076)

8th AJCC prognostic staging system	7th AJCC staging system
	IA		IB		IIA		IIB		IIIA		IIIB		IIIC
	No.	%	No.	%	No.	%	No.	%	No.	%	No.	%	No.	%
IB	12,972	7.7	809	0.5	22,902	13.6	2,303	1.4	504	0.3
IIA	9,842	5.9	372	0.2	6,776	4.0			954	0.6
IIB					4,524	2.7	90	0.1	4,785	2.8
IIIA					8,922	5.3	2,721	1.6	449	0.3	192	0.1	272	0.2
IIIB							1,459	0.9	3,784	2.3	1,173	0.7	1,819	1.1
IIIC							2,989	1.8	2,421	1.4	2,371	1.4	3,114	1.9

Abbreviation: AJCC, American Joint Committee on Cancer.

Table 3 Cox proportional hazards model for the 7th AJCC staging system and 8th AJCC prognostic staging system for breast cancer-specific survival (n=168,076)

Factors	7th staging system				8th prognostic staging system
	Univariate Cox analysis		Multivariate Cox analysis		Univariate Cox analysis
	HR (95% CI)	P-value	HR (95% CI)	P-value	HR (95% CI)	P-value
Stage
IA	Reference		Reference		Reference
IB	1.92 (1.46, 2.53)	<0.001	1.97 (1.50, 2.60)	<0.001	2.92 (2.48, 3.42)	<0.001
IIA	3.95 (3.56, 4.38)	<0.001	2.78 (2.50, 3.08)	<0.001	6.51 (5.55, 7.63)	<0.001
IIB	11.43 (10.21, 12.81)	<0.001	5.30 (4.71, 5.97)	<0.001	9.15 (7.71, 10.85)	<0.001
IIIA	12.42 (11.19, 13.78)	<0.001	8.88 (7.98, 9.87)	<0.001	16.31 (14.08, 18.89)	<0.001
IIIB	32.89 (29.38, 36.83)	<0.001	20.09 (17.90, 22.55)	<0.001	24.81 (21.42, 28.74)	<0.001
IIIC	27.40 (24.61, 30.50)	<0.001	18.54 (16.62, 20.69)	<0.001	60.55 (52.96, 69.24)	<0.001
Grade
I	Reference		Reference		_
II	3.00 (2.60, 3.45)	<0.001	1.77 (1.53, 2.04)	<0.001
III–IV	11.59 (10.14, 13.25)	<0.001	3.27 (2.84, 3.78)	<0.001
ER status
Positive	Reference		Reference		_
Negative	4.63 (4.38, 4.90)	<0.001	1.55 (1.43, 1.67)	<0.001
PR status
Positive	Reference		Reference		_
Negative	5.00 (4.72, 5.31)	<0.001	1.98 (1.82, 2.15)	<0.001
HER2 status
Positive	Reference		Reference		_
Negative	0.88 (0.82, 0.95)	<0.001	1.84 (1.70, 1.99)	<0.001

Abbreviations: AJCC, American Joint Committee on Cancer; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor.

Table 4 Three-year BCSS and OS according to stage (n=168,076)

Stage	AJCC 7		AJCC 8		3-year BCSS (%)		3-year OS (%)
	No.	%	No.	%	AJCC 7	AJCC 8	AJCC 7	AJCC 8
IA	88,985	52.9	69,557	41.4	99.2	99.5	96.9	97.3
IB	4,567	2.7	39,490	23.5	98.3	98.7	96.8	95.7
IIA	43,124	25.7	17,944	10.7	96.6	96.9	93.2	94.3
IIB	9,562	5.7	9,399	5.6	90.1	95.6	87.1	92.8
IIIA	12,897	7.7	12,556	7.5	89.5	92.3	87.1	89.2
IIIB	3,736	2.2	8,235	4.9	75.2	88.8	68.5	85.5
IIIC	5,205	3.1	10,895	6.5	78.9	73.7	75.5	69.9

Abbreviations: AJCC, American Joint Committee on Cancer; OS, overall survival; BCSS, breast cancer-specific survival.

Figure 1 The AJCC staging systems predict survival for primary breast cancer patients and indicate the number of patients at risk.

Notes: The 7th AJCC staging system: BCSS (A) and OS (C). The 8th AJCC prognostic staging system: BCSS (B) and OS (D).

Abbreviations: AJCC, American Joint Committee on Cancer; OS, overall survival; BCSS, breast cancer-specific survival.

Table 5 Three-year BCSS and OS according to the 8th AJCC prognostic staging system

	IA			IB			IIA			IIB			IIIA			IIIB			IIIC
	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value	No. (%)	Rate (%)	P-value
Ref (AJCC 7)	17,797 (20.0)	99.0		914 (20.0)	97.4		8,625 (20.0)	96.6		1,913 (20.0)	91.1		2,580 (20.0)	88.4		748 (20.0)	71.5		1,041 (20.0)	78.9
IA (AJCC 8)	52,949 (59.5)	99.5	<0.001	2,703 (59.2)	99.6	<0.001
IB (AJCC 8)	10,350 (11.6)	99.1	0.904	648 (14.2)	97.5	0.980	18,271 (42.4)	98.7	<0.001	1,817 (19.0)	98.0	<0.001	415 (3.2)	94.2	0.073
IIA (AJCC 8)	7,889 (8.9)	97.2	<0.001	302 (6.6)	91.9	0.002	5,477 (12.7)	97.2	0.856				764 (5.9)	97.7	<0.001
IIB (AJCC 8)							3,660 (8.5)	95.4	0.364	79 (0.8)	96.6	0.974	3,802 (29.5)	95.6	<0.001
IIIA (AJCC 8)							7,091 (16.4)	91.6	<0.001	2,194 (22.9)	93.8	0.025	357 (2.8)	90.8	0.406	162 (4.3)	90.7	0.010	219 (4.2)	94.1	0.208
IIIB (AJCC 8)										1,163 (12.2)	85.7	0.009	3,054 (23.7)	88.7	1.000	930 (24.9)	88.0	<0.001	1,449 (27.8)	92.2	<0.001
III C (AJCC 8)										2,396 (25.1)	81.6	<0.001	1,925 (14.9)	75.8	<0.001	1,896 (50.8)	69.0	<0.001	2,496 (48.0)	69.6	<0.001
Ref (AJCC 7)	17,797 (20.0)	97.0		914 (20.0)	94.7		8,625 (20.0)	93.6		1,913 (20.0)	88.8		2,580 (20.0)	86.5		748 (20.0)	67.4		1,041 (20.0)
IA (AJCC 8)	52,949 (59.5)	97.2	0.005	2,703 (59.2)	98.3	<0.001
IB (AJCC 8)	10,350 (11.6)	96.9	0.996	648 (14.2)	95.3	0.991	18,271 (42.4)	95.0	<0.001	1,817 (19.0)	95.0	<0.001	415 (3.2)	92.6	0.224
IIA (AJCC 8)	7,889 (8.9)	95.0	<0.001	302 (6.6)	95.8	0.135	5,477 (12.7)	93.7	0.997				764 (5.9)	95.8	<0.001
IIB (AJCC 8)							3,660 (8.5)	91.8	0.196	79 (0.8)	92.8	0.836	3,802 (29.5)	93.2	<0.001
IIIA (AJCC 8)							7,091 (16.4)	88.7	<0.001	2,194 (22.9)	90.7	0.238	357 (2.8)	87.1	0.979	162 (4.3)	84.5	0.286	219 (4.2)	75.4	0.263
IIIB (AJCC 8)										1,163 (12.2)	82.6	0.013	3,054 (23.7)	86.5	1.000	930 (24.9)	79.2	<0.001	1,449 (27.8)	91.0	<0.001
IIIC (AJCC 8)										2,396 (25.1)	78.8	<0.001	1,925 (14.9)	72.7	<0.001	1,896 (50.8)	62.4	<0.001	2,496 (48.0)	89.6	<0.001

Note: The bold values emphasize the significant statistical difference.

Abbreviations: AJCC, American Joint Committee on Cancer; OS, overall survival; BCSS, breast cancer-specific survival.

Figure 2 The AJCC staging systems predict breast cancer-specific survival for primary breast cancer patients and indicate the proportion of patients at risk.

Notes: In order to further estimate the prognostic accuracy of the 8th AJCC prognostic staging system, patients from every stage in the 7th AJCC were randomly separated into two parts: 80% patients were staged according to the 8th AJCC prognostic staging system and the other 20% patients were the 7th stage as the reference. (A) 7th stage IA, (B) 7th stage IB, (C) 7th stage IIA, (D) 7th stage IIB, (E) 7th stage IIIA, (F) 7th stage IIIB, and (G) 7th stage IIIC.

Abbreviation: AJCC, American Joint Committee on Cancer.

Table 6 Akaike’s information criterion (AIC)

Variables	7th AJCC staging system				8th AJCC prognostic staging system
	HR (95% CI)	χ^2	P-value	AIC	HR (95% CI)	χ^2	P-value	AIC
Age	1.02 (1.02, 1.03)	506.44	<0.001	101569.38	1.03 (1.03, 1.03)	729.82	<0.001	99317.24
Stage
IA	Reference				Reference
IB	2.07 (1.58, 2.73)	27.05	<0.001		3.05 (2.60, 3.58)	185.58	<0.001
IIA	4.16 (3.75, 4.61)	728.46	<0.001		6.93 (5.91, 8.13)	566.34	<0.001
IIB	12.78 (11.41, 14.33)	1918.47	<0.001		10.11 (8.52, 12.00)	703.69	<0.001
IIIA	14.19 (12.78, 15.76)	2453.31	<0.001		18.51 (15.98, 21.45)	1510.28	<0.001
IIIB	33.20 (29.65, 37.17)	3689.94	<0.001		27.85 (24.04, 32.26)	1963.85	<0.001
IIIC	29.95 (26.89, 33.35)	3830.94	<0.001		70.33 (61.49, 80.45)	3851.01	<0.001