Negative axillary ultrasound in primary breast cancer: how reassured should we really be?

Axillary ultrasound has become an important adjunct in the staging of breast cancer in recent years. We retrospectively studied a sample of 155 women with invasive breast cancer and normal axillary ultrasound to investigate whether the characteristics of the primary tumour could predict the likelihood of false negative axillary ultrasound.

Screening and symptomatic patients were identified from pathology records and information collated from pathology and imaging records.

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).

There are significant differences in tumour characteristics between women with true negative and those with false negative axillary ultrasound in terms of size, primary tumour histological type and presence of lymphovascular invasion. In particular, axillary assessment in primary lobular carcinoma may be more difficult and a negative result should be interpreted with caution.