Table 2.

Multivariable Cox regression analysis of breast cancer-specific survival (BCSS) in patients with HR+/HER2− or HR+/HER2+ mBC

Characteristic	HR+/HER2− cohort (n = 11,467)			HR+/HER2+ cohort (n = 3260)
	HR	95% CI	p-value	HR	95% CI	p-value
Study period
Pre-2015a	Reference			Reference
Post-2015b	0.896	0.849–0.946	< 0.001	0.954	0.855–1.064	0.397
Adjusted post-2015b,c	0.895	0.847–0.946	< 0.001	0.933	0.834–1.044	0.229
Age at diagnosis
18–44 years	Reference			Reference
45–64 years	1.29	1.16–1.42	< 0.001	1.69	1.41–2.03	< 0.001
65–84 years	1.56	1.41–1.73	< 0.001	2.52	2.08–3.06	< 0.001
≥ 85 years	2.47	2.15–2.84	< 0.001	4.28	3.19–5.74	< 0.001
Race and ethnicity
Non-Hispanic White	Reference			Reference
Non-Hispanic Black	1.33	1.22–1.44	< 0.001	1.36	1.15–1.59	< 0.001
Non-Hispanic Asian or Pacific Islander	0.94	0.84–1.06	0.302	1.09	0.88–1.35	0.447
Hispanic	0.99	0.91–1.09	0.907	1.06	0.89–1.27	0.509
American Indian/Alaska Native/Unknown	0.59	0.40–0.87	0.008	0.70	0.33–1.47	0.344
SEER geographic regiond
Big metro/metro/urban	Reference			Reference
Less urban/rural	1.03	0.93–1.14	0.576	1.01	0.83–1.24	0.891
SEER registry sitee
Alaska natives	–	–	–	–	–	–
California	Reference			Reference
Connecticut	0.92	0.80–1.06	0.259	0.63	0.45–0.88	0.007
Georgia	1.06	0.96–1.17	0.238	1.14	0.95–1.36	0.161
Hawaii	1.13	0.92–1.41	0.252	1.52	1.00–2.31	0.049
Iowa	1.03	0.89–1.20	0.707	0.68	0.48–0.98	0.036
Kentucky	1.07	0.93–1.22	0.336	1.11	0.86–1.44	0.434
Louisiana	1.01	0.89–1.15	0.896	1.02	0.80–1.30	0.887
New Jersey	1.06	0.97–1.16	0.210	0.95	0.79–1.14	0.559
New Mexico	1.16	0.96–1.41	0.132	1.07	0.74–1.54	0.723
Seattle (Puget Sound)	1.00	0.88–1.13	0.980	0.84	0.62–1.14	0.250
Utah	1.10	0.92–1.32	0.297	1.01	0.72–1.42	0.956
Median household income
< $55,000	Reference			Reference
$55,000–$64,999	0.97	0.89–1.06	0.523	0.99	0.82–1.20	0.952
$65,000–$74,999	0.96	0.86–1.06	0.400	0.94	0.77–1.15	0.558
≥ $75,000	0.88	0.79–0.97	0.011	0.93	0.76–1.14	0.490
Marital status
Single (never married)	Reference			Reference
Married/unmarried living with domestic partner	0.80	0.74–0.86	< 0.001	0.83	0.72–0.96	0.010
Divorced/separated/ widowed	1.03	0.95–1.11	0.501	1.14	0.97–1.34	0.105
Unknown	0.92	0.80–1.05	0.194	0.98	0.75–1.27	0.849

BCSS breast cancer-specific survival, CI confidence interval, HER2 human epidermal growth factor receptor 2, HR hazard ratio, HR+hormone receptor, mBC, metastatic breast cancer, SEER Surveillance, Epidemiology, and End Results

^aPre-2015 consists of patients diagnosed between 2010 and 2013 (with follow-up to December 31, 2014)

^bPost-2015 consists of patients diagnosed between 2015 and 2018 (with follow-up to December 31, 2019)

^cMultivariable adjusted hazard ratio. Results were adjusted for age at diagnosis, race and ethnicity, SEER geographic region, SEER registry site, median household income, and marital status

^d“Missing/unknown” excluded in each model due to low number of patients in this category

^e“Alaska Natives” excluded in each model due to low number of patients in this category