Table 1.

Baseline characteristics^a of women with bone metastasis from breast cancer eligible for initiating, interrupting, or reinitiating BMAs

Variable	Women with bone metastases from breast cancer		Subset who initiated BMA treatment		Subset who interrupted BMA treatment
	N	%	N	%	N	%
Total	589	100	412	100	258	100
Year of index date
2013	290	49.2	160	38.8	43	16.7
2014	299	50.8	221	53.6	101	39.1
2015	–	–	29	7.0	98	38.0
2016	–	–	2	0.5	16	6.2
Age (years)
18–39	29	4.9	22	5.3	14	5.4
40–49	79	13.4	52	12.6	34	13.2
50–64	215	36.5	155	37.6	99	38.4
65+	266	45.2	183	44.4	111	43.0
Race
White	356	60.4	261	63.3	166	64.3
Black	60	10.2	34	8.3	24	9.3
Asian	14	2.4	10	2.4	9	3.5
Other	88	14.9	55	13.3	34	13.2
Missing	71	12.1	52	12.6	25	9.7
History of SREs
Pathological fracture	72	12.2	86	20.9	66	25.6
Spinal cord compression	9	1.5	7	1.7	5	1.9
External beam radiation therapy	9	1.5	87	21.1	92	35.7
Bone surgery	19	3.2	24	5.8	24	9.3
Other sites of metastases
Lung	69	11.7	72	17.5	25	9.7
Brain	15	2.5	21	5.1	16	6.2
Distant lymph node	47	8	67	16.3	24	9.3
Prior cancer treatment
Chemotherapy	21	3.6	151	36.7	101	39.1
Colony-stimulating factor	14	2.4	47	11.4	43	16.7
Hormonal therapy	73	12.4	216	52.4	97	37.6
Renal disease	86	14.6	109	26.5	79	30.6
eGFR (mL/min)
<60	32	5.4	34	8.3	21	8.1
≥60	121	20.5	110	26.7	73	28.3
Missing	436	74	268	65.0	164	63.6
ER status
Positive	490	83.2	353	85.7	221	85.7
Negative	93	15.8	58	14.1	37	14.3
Unknown	6	1	1	0.2	0	0.0
PR status
Positive	410	69.6	296	71.8	195	75.6
Negative	167	28.4	110	26.7	60	23.3
Unknown	12	2	6	1.5	3	1.2
HER2 status
Positive	122	20.7	78	18.9	55	21.3
Negative	443	75.2	323	78.4	198	76.7
Unknown/equivocal	24	4.1	11	2.7	5	1.9
Insurance payer
Commercial health insurance plan	137	23.3	102	24.8	69	26.7
Medicaid	18	3.1	12	2.9	8	3.1
Medicare	25	4.2	10	2.4	5	1.9
Missing	132	22.4	89	21.6	40	15.5
Multiple	192	32.6	140	34.0	97	37.6
Other	85	14.4	59	14.3	38	14.7

Notes:

^aBaseline characteristics were measured in the 6-month baseline period or using all available data prior to the index date to identify chronic comorbidities. Baseline characteristics were updated at the start of BMA treatment and on the date of BMA interruption. “−” indicates that there were zero patients in this category.

Abbreviations: BMA, bone-modifying agent; eGFR, estimated glomerular filtration rate; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor; SRE, skeletal-related event.