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

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)