Table 2.

Descriptive statistics of distributions of tumor characteristics comparing interval cancers to screen-detected cancers, interval cancers to screen-detected cancers limited to nondense breasts and interval cancers to screen-detected cancers limited to dense breasts

	All (n = 1,400)			Nondense, PD <25% (n = 1,055)			Dense, PD ≥25% (n = 345)
	SD cancer (n = 1,115)	IC (n = 285)	P value	SD cancer (n = 867)	IC (n = 188)	P value	SD cancer (n = 248)	IC (n = 97)	P value
Mean tumor size (mm)	14.4	20.5	<0.001	14.2	19.6	<0.001	15.2	22.4	<0.001
Lymph node metastasis, n (%)			<0.001			<0.001			0.001
Positive	240 (22%)	109 (39%)		190 (22%)	72 (39%)		50 (20%)	37 (38%)
Negative	856 (78%)	171 (61%)		660 (78%)	111 (61%)		196 (80%)	60 (62%)
ER status, n (%)			0.020			0.054			0.150
Positive	627 (83%)	162 (76%)		492 (82%)	99 (75%)		135 (84%)	63 (77%)
Negative	131 (17%)	52 (24%)		106 (18%)	33 (25%)		25 (16%)	19 (23%)
PR status, n (%)			0.008			0.018			0.133
Positive	536 (72%)	130 (62%)		420 (71%)	78 (60%)		116 (74%)	52 (65%)
Negative	211 (28%)	79 (38%)		171 (29%)	51 (40%)		40 (26%)	28 (35%)
Grade, n (%)			<0.001			0.008			0.012
1	147 (20%)	20 (11%)		116 (20%)	15 (14%)		31 (19%)	5 (6%)
2	333 (45%)	71 (37%)		265 (45%)	40 (36%)		68 (42%)	31 (39%)
3	268 (36%)	99 (52%)		205 (35%)	56 (50%)		63 (39%)	43 (54%)
Histological classification, n (%)			0.703			0.872			0.441
Ductal	813 (73%)	206 (74%)		640 (74%)	134 (72%)		173 (71%)	72 (76%)
Lobular	125 (11%)	35 (13%)		92 (11%)	22 (12%)		33 (13%)	13 (14%)
Other	173 (16%)	39 (14%)		134 (15%)	29 (16%)		39 (16%)	10 (11%)
Proliferation rate			<0.001			<0.001			0.523
High	108 (25%)	52 (42%)		83 (25%)	36 (48%)		25 (28%)	16 (33%)
Low	316 (75%)	71 (58%)		252 (75%)	39 (52%)		64 (72%)	32 (67%)

^aIC, interval cancer; ER, estrogen receptor; PD, percentage density; PR, progesterone receptor; SD, screen-detected.