Table 4.

Breast cancer–specific MRRs stratified by age at diagnosis, California, 2005–2014

	Younger (18–49)			Older (50+)
	Number of deaths due to breast cancer	MRR (95% CI)^a	MRR (95% CI)^b	Number of deaths due to breast cancer	MRR (95% CI)^a	MRR (95% CI)^b
All	2,236			6,233
Tumor subtype
HR⁺/HER2^–	820	Reference	Reference	2,781	Reference	Reference
HR⁺/HER2⁺	236	1.11 (0.96–1.29)	0.80 (0.69–0.93)	598	1.69 (1.55–1.85)	1.05 (0.95–1.15)
HR^–/HER2⁺	214	2.45 (2.11–2.85	1.37 (1.15–1.62)	476	2.86 (2.60–3.16)	1.28 (1.14–1.43)
Triple negative	738	3.88 (3.51–4.29)	2.50 (2.19–2.86)	1,518	4.26 (4.00–4.54)	2.35 (2.17–2.53)
Unclassified	228	1.29 (1.11–1.49)	1.11 (0.96–1.29)	860	1.56 (1.44–1.68)	1.25 (1.16–1.36)
	P interaction = 0.0008^c
NCICC
No	1,901	Reference	Reference	5,784	Reference	Reference
Yes	335	1.08 (0.96–1.22)	1.00 (0.89–1.13)	449	0.94 (0.86–1.04)	0.84 (0.76–0.93)
	P interaction = 0.003^c
Guideline-concordant treatment
Yes	1,409	Reference	Reference	2,879	Reference	Reference
No	230	1.25 (1.09–1.44)	1.20 (1.03–1.40)	657	1.47 (1.35–1.60)	1.49 (1.36–1.63)
Not available	590	0.32 (0.29–0.36)	1.00 (0.88–1.15)	2,683	0.31 (0.29–0.32)	1.14 (1.05–1.24)
Unknown	7	0.95 (0.45–2.00)	0.59 (0.27–1.30)	14	1.09 (0.65–1.85)	0.79 (0.45–1.40)
	P interaction = 0.015^c

↵^aAdjusted for year at diagnosis.
↵^bStratified by AJCC stage, and adjusted for year of diagnosis, age at diagnosis (continuous), marital status, race/ethnicity, insurance status, nSES, lymph node involvement, tumor size, tumor grade, tumor histology, and clustering by block group.
↵^cP for interaction between age group (younger and older) and tumor subtype, NCICC, or guideline-concordant treatment (excluding unknown) from a model which included all significant interactions with age group.