Breast cancer diagnosis in a specialised breast clinic: Are cancers detected by ultrasound alone less aggressive?

INTRODUCTION: The aim of this study was to determine the relationship between the way breast cancer is diagnosed and its prognostic features.

METHODS: We studied new primary invasive and non-invasive breast cancers (670) diagnosed between 2013 and 2015 where detection included at least clinical examination, mammography and breast ultrasound (BUS). The cancers were classified into six Diagnostic Groups according to the results of each modality.

RESULTS: Overall, 79% of cancers were positive on mammography, but another 20% were diagnosed on BUS after a negative mammogram. The largest group (37.6% of cases), had all three modalities positive (Group 1). BUS was the only modality positive in 14.6% (Group 4). Mammography alone was positive in 21.2%, of which 73.9% were ductal carcinoma in situ (DCIS). Invasive lobular carcinoma comprised 9.6% of the groups where mammography was positive, but 16.5% of the groups where mammography was negative and BUS positive. Dense breast tissue was more common in the groups where mammography was negative and BUS positive. Invasive cancers comprised 82.7% of Group 4 and 95.2% of Group 1. For those in Group 4, the average size (10.2 mm) and the percentages with lymphovascular invasion (11.1%), lymph node involvement (17.3%) and poor differentiation (12.3%) were less than half the corresponding figures for Group 1 (27.3 mm, 35%, 44%, 44%).

CONCLUSION: This study illustrates the complementary benefits of mammography and BUS, especially where breast density is high. Tumours diagnosed by BUS alone had better prognostic features in terms of size, lymphovascular invasion, lymph node status, differentiation and hormone receptors, compared with cancers where all three modalities were positive.