Table 2.

Association of patient/tumor characteristics with HER2 somatic mutation in the full cohort of breast cancer patients (n = 1348)

Characteristic	No. of patients	Non‐carriers (n = 1321)		Carriers (n = 27)		a P‐value
		No.	%	No.	%
Age, years
≤50	596	589	44.6	7	25.9	<0.001
>50	752	732	55.4	20	74.1
Tumor size, cm
≤2	515	504	38.2	11	40.7	0.789
>2	831	815	61.8	16	59.3
Unknown	2	2		0
Tumor grade
1	146	144	12.0	2	8.0	0.790
2	907	888	74.1	19	76.0
3	170	166	13.9	4	16.0
Unknown	125	123		2
Tumor stage
I	316	308	24.1	8	29.6	0.793
II	764	749	58.7	15	55.6
III	224	220	17.2	4	14.8
Unknown	44	44		0
Lymph node status
Negative	742	724	56.7	18	66.7	0.298
Positive	563	554	43.3	9	33.3
Unknown	43	43		0
ER status
Negative	388	378	28.7	10	37.0	0.347
Positive	954	937	71.3	17	63.0
Unknown	6	6		0
PR status
Negative	530	514	39.4	16	59.3	0.037
Positive	802	791	60.6	11	40.7
Unknown	16	16		0
HER2 status
Negative	953	931	72.8	22	81.5	0.314
Positive	353	348	27.2	5	18.5
Unknown	42	42		0
Triple‐negative status
No	1144	1124	85.5	20	74.1	0.098
Yes	198	191	14.5	7	25.9
Unknown	6	6		0
Surgery type
BCS	478	472	36.7	6	22.2	0.122
Mastectomy	835	814	63.3	21	77.8
Unknown	35	35		0
Trastuzumab use
No	1286	1260	95.4	26	96.3	1.000
Yes	62	61	4.6	1	3.7
Adjuvant therapy
C	374	362	28.6	12	44.4	0.060
E	246	239	18.9	7	25.9
C plus E	672	664	52.5	8	29.6
None	56	56		0

^aPatients with HER2 somatic mutations versus patients with wild‐type.

BCS, breast‐conserving surgery; C, chemotherapy; E, endocrine therapy; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor.