Table 1. Baseline characteristics of the 412 patients in the primary analysis group.

	n	%
Patients who had mammography	364	88.3
Patients who had fine-needle aspiration	365	88.6
Patients who had a core biopsy	55	13.3
Age at first surgery (years) – median (Q1, Q3)	43	(40, 46)
(min., max.)		(22, 54)
LMP group at first surgery
0–4 days	64	15.5
5–9 days	70	17.0
10–14 days	61	14.8
15–19 days	62	15.0
20–24 days	71	17.2
25–29 days	39	9.5
30+ days	31	7.5
Unidentifiablea	14	3.4
Type of first surgery
Excision biopsy	74	18.0
Lumpectomy	197	47.8
Mastectomy	138	33.5
Axillary procedure only	1	0.2
Neoadjuvant therapy	1	0.2
Missing	1	0.2
Type of axillary procedure at first surgery
None	100	24.3
Sample	69	16.7
Clearance	243	59.0
Further surgery required	134	32.5
Adjuvant treatment received	402	97.6
Chemotherapy given	278	69.2
Hormone therapy given	278	69.2
Radiotherapy given	320	79.6
Histological grade
I	59	14.3
II	181	43.9
III	154	37.4
Missing	18	4.4
Tumour size (mm) – median (Q1, Q3)	20	(15, 30)
(min., max.)		(0.5, 150)
Number of nodes sampled – median (Q1, Q3)	11	(7, 16)
(min., max.)		(0, 36)
Nodal status
Positive	208	50.5
Negative	193	46.8
Missing	11	2.7
NPI prognostic groups – three categories
Good	110	26.7
Moderate	176	42.7
Poor	95	23.1
Missing	31	7.5

LMP=last menstrual period; NPI=Nottingham Prognostic Index.

^aPatients whose LMP date or surgery date is missing, or who had neoadjuvant therapy, are classed as having an unidentifiable LMP group.