Risk factors and natural history of breast cancer in younger Chinese women

Table 1 Sociodemographics and breast screening habits of the total patient cohort (n = 7152)

	< 40 yr (n = 1008) n (%)		≥40 yr (n = 6144) n (%)		P value
Age
< 20	1	(0)			--
20-29	84	(1.2)
30-39	923	(12.9)
40-49			2 978	(41.6)-
50-59			2 102	(29.4)
60-69			698	(9.8)
70-79			268	(3.7)
80+			98	(1.4)
Education level
No schooling	4	(0.4)	344	(5.7)	χ2 = 473.730, bP < 0.001
Primary	47	(4.7)	1 544	(25.5)
Secondary	488	(49.3)	2 986	(49.4)
Matriculation	133	(13.4)	425	(7)
Undergraduate/postgraduate	318	(32.1)	748	(12.4)
Occupation
Professional/Clerical	608	(63)	1 845	(31)	χ2 = 412.754, bP < 0.001
Non-clerical/Labor	126	(13.1)	1 298	(21.8)
Self-employed	45	(4.7)	190	(3.2)
Housewife	170	(17.6)	2 043	(34.3)
Retired/Unemployed	16	(1.7)	585	(9.8)
Monthly household income
< HK$10000	77	(10.4)	837	(22.5)	χ2 = 88.503, bP < 0.001
HK$10000-29999	290	(39.1)	1 591	(42.8)
≥ HK$30000	375	(50.5)	1 287	(34.6)
Breast screening habits
Breast self examination
Never	332	(33.8)	2 359	(39.7)	χ2 = 13.136, bP = 0.001
Occasional	428	(43.6)	2 295	(38.6)
Monthly	222	(22.6)	1 288	(21.7)
Clinical breast examination
Never	380	(38.5)	2 625	(44.1)	χ2 = 10.934, bP = 0.004
Occasional	132	(13.4)	718	(12.1)
Regular1	476	(48.2)	2 611	(43.9)
Mammogram
Never	--		3 929	(66.1)	--
Occasional	--		554	(9.3)
Regular1	--		1 463	(24.6)
Ultrasound
Never	--		4 029	(70.3)	--
Occasional	--		520	(9.1)
Regular1	--		1 179	(20.6)

¹Regular means having breast examinations annually, or once every 2-3 years.

Table 2 Associated risk factors for breast cancer development in the total patient population (n = 7152)

	< 40 yr (n = 1008) n (%)		≥40 yr (n = 6144) n (%)		P value
Family history of breast cancer
Yes	178	(17.7)	891	(14.5)	χ2 = 6.788, aP = 0.010
No	830	(82.3)	5 253	(85.5)
Lifestyle-related risk factors
Lack of exercise (< 3h/wk)
Yes	861	(85.4)	4 497	(73.2)	χ2 = 68.848, bP < 0.001
No	147	(14.6)	1 647	(26.8)
High level of stress (> 50% of time)
Yes	465	(46.1)	2 179	(35.5)	χ2 = 42.272, aP < 0.001
No	543	(53.9)	3 965	(64.5)
Being overweight/obese (BMI ≥ 23.0)
Yes	241	(23.9)	2 344	(38.2)	χ2 = 76.104, bP < 0.001
No	767	(76.1)	3 800	(61.8)
Diet rich in meat/dairy products
Yes	204	(20.2)	791	(12.9)	χ2 = 39.205, bP < 0.001
No	804	(79.8)	5 353	(87.1)
Frequently night shifts
Yes	81	(11.4)	285	(9.3)	χ2 = 2.958, P = 0.091
No	632	(88.6)	2 796	(90.7)
Alcohol drinking habit
Yes	77	(7.7)	316	(5.2)	χ2 = 10.008, bP = 0.002
No	925	(92.3)	5 747	(94.8)
Hormone-related risk factors
Breastfeeding
Yes	226	(46.3)	1 933	(40.9)	χ2 = 5.249, aP = 0.023
No	262	(53.7)	2 788	(59.1)
Nulliparity
Yes	381	(43.3)	1 042	(17.8)	χ2 = 297.601, bP < 0.001
No	499	(56.7)	4 805	(82.2)
First live birth age after 35
Yes	21	(4.3)	238	(5.1)	χ2 = 0.630, P = 0.514
No	469	(95.7)	4 420	(94.9)
Early menarche (< 12 yr old)
Yes	197	(20.7)	759	(13.2)	χ2 = 37.243, bP < 0.001
No	755	(79.3)	4 982	(86.8)
Use of hormone replacement therapy
Yes	5	(8.1)	376	(11.7)	χ2 = 0.778, P = 0.546
No	57	(91.9)	2 841	(88.3)

Table 3 Differences in the pathological characteristics of patients with invasive breast tumours (n = 5523)

	< 40 yr (n = 706) n(%)	≥40 yr (n = 4 817) n(%)	P value
Method of detection
Self-detected	589 (94.1)	3962 (90.3)	χ2 = 9.513, bP = 0.001
Screen-detected1	37 (5.9)	427 (9.7)
Presenting symptoms (for self-detected cancers)
Lump	553 (93.9)	3729 (94.1)	χ2 = 0.049, P = 0.780
Pain	29 (4.9)	173 (4.4)	χ2 = 0.375, P = 0.521
Nipple discharge	30 (5.1)	118 (3)	χ2 = 7.291, aP = 0.012
Nipple retraction	5 (0.8)	75 (1.9)	χ2 = 3.237, P = 0.090
Skin change	3 (0.5)	37 (0.9)	χ2 = 1.061, P = 0.475
Axillary node	5 (0.8)	23 (0.6)	NA2
Asymmetry	2 (0.3)	11 (0.3)	NA2
Duration of onset of symptoms (for self-detected cancers)
< 1 mo	93 (39.9)	536 (39.6)	χ2 = 0.466, P = 0.926
1-3 mo	90 (38.6)	515 (38.1)
4-12 mo	33 (14.2)	212 (15.7)
> 12 mo	17 (7.3)	89 (6.6)
Cancer stage
Early stage (Stage I-IIB)	603 (88.2)	3900(83)	χ2 = 11.490, bP = 0.001
Advanced stage (Stage IIIA –IV)	81 (11.8)	797(17)
Tumour size4
Mean ± SD (cm)	2.15 ± 1.30	2.24 ± 1.49	T = -1.514, P = 0.130
Median (cm)3	1.9	2	P = 0.065
IQR (cm)	1.40-2.70	1.40-2.80	--
≤ 2.0	361 (55.4)	2283 (51.5)	χ2 = 3.407, P = 0.071
> 2.0	291 (44.6)	2150 (48.5)
Bloom and Richardson grade4
1	80 (12.9)	806 (19.2)	χ2 = 24.682, bP < 0.001
2	258 (41.5)	1865 (44.3)
3	284 (45.7)	1537 (36.5)
Lymphovascular invasion4	229 (39.6)	1336 (33.2)	χ2 = 8.972, bP = 0.003
Disease4
Multifocality	104 (15.7)	463 (10.3)	χ2 = 17.472, bP < 0.001
Multicentricity	21 (3.2)	120 (2.7)	χ2 = 0.597, P = 0.442
Estrogen receptor + ve (ER+)4	481 (75)	3389 (75.6)	χ2 = 0.100, P = 0.768
Progesterone receptor +ve (PR+)4	400 (62.7)	2836 (63.5)	χ2 = 0.162, P = 0.693
Human Epidermal Growth Factor Receptor 2 +ve (HER2+)4	151 (28.5)	970 (26.8)	χ2 = 0.728, P = 0.402
Triple negative subtype4	74 (14.0)	450 (12.5)	χ2 = 1.000, P = 0.327
Nodal status (no. of positive nodes)4
0	409 (61.9)	2680 (59.4)	χ2 = 6.908, P = 0.075
1-3	184 (27.8)	1198 (26.6)
4-9	44 (6.7)	420 (9.3)
10+	24 (3.6)	212 (4.7)

¹Screen-detected includes monthly self-exam, clinical breast exam (routine checkups), mammography or ultrasound screening;

²Chi-square test was not available due to the small number of patients;

³Mann-Whitney U test was used;

⁴227 patients underwent neoadjuvant therapy and did not have pathology reports, thus had missing values for these parameters: tumour size, Bloom and Richardson grade, presence of lymphovascular invasion, multifocality, multicentricity, endocrine receptor status, human epidermal growth factor receptor 2 status, and nodal status.

Table 4 Treatments received by patients with invasive breast tumours (n = 5523)

	< 40 yr (n = 706) n (%)	≥40 yr (n = 4817) n (%)	P value
Surgery
Breast conserving surgery	324 (46.1)	1638 (34.3)	χ2 = 36.921, bP < 0.001
Mastectomy	379 (53.9)	3135 (65.7)
Reconstruction
Yes	135 (35.7)	367 (11.7)	χ2 = 158.189, bP < 0.001
No	243 (64.3)	2762 (88.3)
Nodal Surgery
Sentinel node biopsy (SNB)	222 (32.2)	1351 (28.7)	χ2 = 8.496, aP = 0.014
Axillary dissection (AD)	336 (48.7)	2572 (54.6)
SNB+AD	132 (19.1)	787 (16.7)
Chemotherapy
Stage I	151 (59.2)	633 (39.7)	χ2 = 34.433, bP < 0.001
Stage IIA	210 (88.6)	1291 (83.8)	χ2 = 3.572, P = 0.067
Stage IIB	97 (100)	631 (91.1)	χ2 = 9.417, bP < 0.001
Stage III	72 (98.6)	664 (93.7)	NA1
Stage IV	8 (100)	69(89.6)	NA1
Radiotherapy (overall)
All patients	496 (72)	3106 (66.2)	χ2 = 9.189, bP = 0.002
BCS patients	306 (96.2)	1522 (95.4)	χ2 = 0.460, P = 0.556
MTX patients	190 (51.6)	1564 (51.2)	χ2 = 0.027, P = 0.912
Irradiated regions (overall)
Breast ± regional lymph nodes	187 (60.1)	998 (46)	χ2 = 21.859, bP < 0.001
Chest wall ± regional lymph nodes	124 (39.9)	1173 (54)
Endocrine therapy	477 (68.7)	3496 (74.2)	χ2 = 9.206, bP = 0.003
Targeted therapy	59 (8.6)	339 (7.2)	χ2 = 1.682, P = 0.211

¹χ²-test was not available due to the small number of patients.