Of the 155 normal ultrasounds, 45 (29%) were positive at axillary surgery.
True and false negative groups were compared in terms of the following: tumour size, pathological type and grade, lymphovascular invasion and oestrogen receptor (ER) status.
Breast tumour size was significantly different, with the average size in the true negative group 21 mm and in the false negative group 30 mm (P < 0.002).
There was no significant difference in tumour grade or ER status. However, the histological type varied significantly between the groups, with excess lobular carcinomas in the false negative group (6 of 110 versus 6 of 45, P < 0.001).
The false negative group was more likely to show lymphovascular invasion in the breast (31% versus 5%, P < 0.001).