MRI appearance of invasive subcentimetre breast carcinoma: benign characteristics are common.

OBJECTIVE: This study was undertaken to examine the characteristics of cancers detected at the earliest possible point on MRI and to determine their significance.

METHODS: This institutional review board-approved Health Insurance Portability and Accountability Act-compliant retrospective study evaluated invasive breast cancers ≤1 cm histologically. MRI was performed within 6 months before diagnosis. Between 1 January 2005 and 31 December 2015, 163 cancers in 161 patients were evaluated. Breast Imaging-Reporting and Data System lesion characteristics were assessed by two radiologists independently. In cases of disagreement, arbitration by a third reader was performed.

RESULTS: Cancers ≤1 cm became more obviously malignant as they enlarged with regard to shape (p = 0.021), margin (p = 0.0006), internal enhancement (p = 0.0158) and kinetics (p = 0.0001). Cancers ≤5 mm had benign characteristics of circumscribed margins in 71% (71/100), round/oval shape in 67% (67/100) and persistent enhancement in 41% (41/100). High T2 signal was found in 17% (28/62), distributed equally among different sizes (p = 0.3920). In ≤5-mm cancers (59%, 12/29), a comparison study to show interval growth was more often needed to determine the need for biopsy. When interval growth determined biopsy, this was evident within 24 months and cancers remained node negative despite this delay.

CONCLUSION: Benign characteristics are present in most invasive cancers ≤5 mm. Small cancers on MRI may need to demonstrate growth to determine need for biopsy. Advances in knowledge: MR lesion characteristics may not be helpful in determining whether small lesions on MR are benign or malignant. However, as 97% of cancers in our study showed interval change when a prior MR for comparison was available, new lesions or increasing size should lead to consideration of biopsy.