Table 1.

Patient, Tumor and Treatment Characteristics

	Breast Radiation
Characteristic	No		Yes		P-valuea
	N	%	N	%
Age
70–74	93	16%	1204	42%	<0.0001
75–79	116	20%	921	32%
≥ 80	373	64%	725	25%
Year of Diagnosis
1993–1999	135	23%	647	23%	0.54
2000–2004	219	38%	1018	36%
2005–2009	228	39%	1185	42%
Derived AJCC T stage
T1mic+T1a	33	5.7%	270	9.5%	<0.0001
T1b	111	19%	644	23%
T1c	233	40%	1306	46%
T2	205	35%	630	22%
Progesterone receptor status
Positive	>32	>5.7%	209	7.3%	0.64
Negative	538	92%	2613	92%
Indeterminate+Not Done+Unknown	<11	<1.9%	28	0.98%
Tumor Histology
Ductal Carcinoma	511	88%	2600	91%	0.03
Lobular Carcinoma	24	4.1%	88	3.1%
Other	47	8.1%	162	5.7%
Histologic grade
Well differentiated	41	7.0%	180	6.3%	0.84
Intermediate/moderate	174	30%	823	29%
Poorly-/Un- differentiated	325	57%	1608	59%
Not determined	35	6.0%	175	6.1%
Comorbidity Indexb
0	144	25%	1163	41%	<0.0001
1	91	16%	444	16%
≥ 2	347	60%	1243	43%
Chemotherapy
Yes	69	12%	822	29%	<0.0001
No	513	88%	2028	71%
Race
White	485	83%	2477	87%	0.02
Black	69	12%	245	8.6%
Hispanic	<11	<1.9%	33	1.2%
Asian	<11	<1.9%	44	1.5%
Other/ Native Amerciand	<11	<1.9%	51	1.8%
Marital status
Married	142	24%	1320	46%	<0.0001
Unmarried	409	70%	1453	51%
Unknown	31	5.3%	77	2.7%
Demographic Region
West	258	44%	1193	42%	0.63
Midwest	82	14%	412	15%
South	110	19%	538	19%
Northeast	133	23%	712	25%
Urban residence
Metro	503	86%	2535	89%	0.08
Urban+Rural	79	14%	315	11%
Census Track Level Povertyc
0.00%–9.99%	345	59%	1921	67%	0.0003
10.00%–19.99%	150	26%	628	22%
20.00%+	87	15%	301	11%

^aP-value is calculated by Chi-square Test except for Race, which is calculated by Fisher's Exact.

^b69 patients’ Medicare Enrollment in the 12 months prior to Breast Cancer Diagnosis were not continuous, CCI were calculated from all the claims existed in Medicare for these 69 patients.

^cZip code poverty level were used for 30 patients with missing census track poverty level

^dThis category also contains a very small number of unknown race subgroup