Relationships Between MRI Breast Imaging‐Reporting and Data System (BI‐RADS) Lexicon Descriptors and Breast Cancer Molecular Subtypes: Internal Enhancement is Associated with Luminal B Subtype

The aim of this study was to determine the associations between breast MRI findings using the Breast Imaging‐Reporting and Data System (BI‐RADS) lexicon descriptors and breast cancer molecular subtypes. In this retrospective, IRB‐approved, single institution study MRIs from 278 women with breast cancer were reviewed by one of six fellowship‐trained breast imagers. Readers reported BI‐RADS descriptors for breast masses (shape, margin, internal enhancement) and non‐mass enhancement (distribution, internal enhancement). Pathology reports were reviewed for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor‐2 (HER2). Surrogates were used to categorize tumors by molecular subtype: ER/PR+, HER2‐ (luminal A); ER/PR+, HER2+ (luminal B); ER/PR‐, HER2+ (HER2); ER/PR/HER2‐ (basal). A univariate logistic regression model was developed to identify associations between BI‐RADS descriptors and molecular subtypes. Internal enhancement for mass and non‐mass enhancement was combined for analysis. There was an association between mass shape and basal subtype (p = 0.039), which was more frequently round (17.1%) than other subtypes (range: 0–8.3%). In addition, there was an association between mass margin and HER2 subtype (p = 0.040), as HER2 cancers more frequently had a smooth margin (33.3%) than other subtypes (range: 4.2–17.1%). Finally, there was an association between internal enhancement and luminal B subtype (p = 0.003), with no cases of luminal B cancer demonstrating homogeneous internal enhancement versus a range of 10.9–23.5% for other subtypes. There are associations between breast cancer molecular subtypes and lesion appearance on MRI using the BI‐RADS lexicon.