Mammographic breast density and risk of breast cancer in women with atypical hyperplasia: an observational cohort study from the Mayo Clinic Benign Breast Disease (BBD) cohort

Table 1 Associations of extent of mammographic breast density with breast cancer risk by levels of benign histologic impression

	Low Density				Medium Density				High Density				p-value^a
Characteristic	N	Obs	Exp	SIR (95% CI)	N	Obs	Exp	SIR (95% CI)	N	Obs	Exp	SIR (95% CI)	p-value^a
Histologic Impression
NP	699	30	40.07	0.75 (0.50, 1.07)	1586	99	80.27	1.23 (1.00, 1.50)	1247	95	56.69	1.68 (1.36, 2.05)	<0.001
PDWA	364	31	22.15	1.40 (0.95, 1.99)	1104	113	58.76	1.92 (1.58, 2.31)	801	78	43.50	1.79 (1.42, 2.24)	0.27
AH	69	12	3.53	3.40 (1.76, 5.93)	231	41	11.77	3.48 (2.50, 4.73)	170	29	8.92	3.25 (2.18, 4.67)	0.96

Standardized incidence ratios and corresponding 95% confidence intervals, comparing the observed number of breast cancer events to those expected based on incidence rates from Iowa SEER data. Analyses account for the effects of age and calendar period
NP non-proliferative disease, PDWA proliferative disease without atypia, AH atypical hyperplasia, N number of individuals, Obs observed number of breast cancer events, Exp expected number of breast cancer events, SIR standardized incidence ratio, CI confidence interval
^a P-value, test of heterogeneity in SIRs across columns

ISSN: 1471-2407