Searching for early breast cancer biomarkers by serum protein profiling of pre-diagnostic serum; a nested case-control study

Table 2 Characteristics of the serum samples

	Cases (n = 68)	Controls (n = 68)	P-value
*Serum sample storage duration (years)**
Mean (SD)	11.2 (1.1)	11.2 (1.1)	0.900^§
Hours in refrigerator ^†
Median (IQR)	22 (21-23)	22 (20-23)	0.845^#
Days at -86°C ^‡
Median (IQR)	8 (6-11)	7 (5-11)	0.429^#

SD: standard deviation; IQR: inter-quartile range; * Until date of experiment; ^† Between collection and centrifugation; ^‡ Between centrifugation and storage at liquid nitrogen; ^§ Independent samples T test; ^# Mann-Whitney U test.

ISSN: 1471-2407