[MRI findings and pathological features of occult breast cancer]

Objective: To investigate the magnetic resonance imaging (MRI) findings and clinicopathological features of primary lesions in patients with occult breast cancer (OBC). Methods: The imaging reports from the Breast Imaging Reporting and Data System in 2013 were retrospectively analyzed to investigate the morphology and the time signal intensity curve (TIC) of breast lesions in patients with OBC. The clinical and pathological characteristics of these patients were also included. Results: A total of 34 patients were enrolled. Among these patients, 24 patients underwent modified radical mastectomy and 18 of them had primary breast carcinoma in pathological sections. MRI detected 17 cases of primary lesions, including six masse lesions with a diameter of 0.6-1.2 cm (average 0.9 cm), and 11 non-mass lesions with four linear distributions, three segmental distributions, three focal distributions, and one regions distribution. Five patients had TIC typeⅠprimary lesions, ten had TIC type Ⅱ primary lesions, and two had TIC type Ⅲ primary lesions. Among all 34 cases, 23 of them had complete results of immunohistochemistry: 11 estrogen receptor (ER) positive lesions (47.8%), tenprogesterone receptor (PR) positive lesions (43.5%), seven human epidermal growth factor receptor 2 (HER-2) positive lesions (30.4%), and 20high expression(>14%) of Ki-67 (87.0%). The proportion of type luminal A was 4.3%, type luminal B was 43.5%, triple negative breast cancer (TNBC) was 30.4%, and HER-2 over expression accounted for 21.7%. Conclusions: The primary lesions of OBC usually manifested as small mass lesions, or focal, linear or segmental distribution of non-mass lesions. The positive rate of ER and PR was low, but the positive rate of HER-2 and the proliferation index of Ki-67 was high. Type luminal B is the most common molecular subtype.