Assessing the usefulness of a novel MRI-based breast density estimation algorithm in a cohort of women at high genetic risk of breast cancer: the UK MARIBS study

Table 4 Breast cancer risk according to MRI percent dense volume and Cumulus and visual assessment percent dense area (Medial-Lateral Oblique view), by BRCA1/BRCA2 genetic status

	No. women	No. cancers	No. pyears	IRR (95% CI) P-value (adjusted age)	IRR (95% CI) P-value (adjusted age, BMI & parity)
*BRCA1 Carriers*
MRI % dense volume	117	21	687	1.84 (0.77, 4.38) 0.17	1.02 (0.26, 4.05) 0.98
Cumulus MLO % dense area	94	16	579	2.72 (0.99, 7.48) 0.053	1.24 (0.35, 4.37) 0.74
VA MLO % dense area	94	16	579	4.03 (1.40, 11.6) 0.010	3.39 (0.94, 12.2) 0.062
*BRCA2 Carriers*
MRI % dense volume	69	18	385	2.06 (0.78, 5.45) 0.15	3.10 (0.77, 12.4) 0.11
Cumulus MLO % dense area	71	15	418	1.66 (0.60, 4.60) 0.33	10.4 (1.58, 68.0) 0.015
VA MLO % dense area	71	15	418	1.75 (0.62, 4.90) 0.29	3.70 (0.64, 21.2) 0.14
*Non-carriers*
MRI % dense volume	361	14	2,532	4.49 (1.16, 17.3) 0.030	2.54 (0.56, 11.6) 0.23
Cumulus MLO % dense area	332	7	2,367	1.13 (0.25, 5.17) 0.87	0.24 (0.04, 1.45) 0.12
VA MLO % dense area	327	7	2,336	1.45 (0.32, 6.66) 0.63	0.43 (0.08, 2.41) 0.34

The non-carrier group includes those who tested negative for a known BRCA1/2 family mutation as well as those in whom no mutation was
detected after a BRCA1/2 mutation screen, because of small numbers.
Pyears = number of person-years in study and follow-up period
IRR = incidence rate ratio for the upper two quartiles relative to the lower two quartiles (the trend test was not attempted due to the small numbers). CI = confidence intervals.

ISSN: 1465-542X