Abstract: Background and purpose: Breast cancer is rare in young women under 30 years old, but in recent years breast cancer patients have become younger and its incidence has increased year by year. The identification of early breast cancer immunohistochemical molecular subtypes can improve the treatment plan. The primary purpose of the present study was to analyze the ultrasonography (US), digital mammography (DM) and digital breast tomosynthesis (DBT) features of breast cancer in very young women (≤30 years old) and the correlation with molecular subtypes. Methods: We performed a retrospective review of imaging and pathological features of consecutive young women under 30 years old who were treated in the Affiliated Hospital of Qingdao University and were diagnosed and histopathologically confirmed with breast cancer from Dec. 2013 to Jul. 2019. Three imaging techniques were used to assess the features of the lesions. DM, DBT and US were available for 139 patients. The imaging findings were evaluated according to the Breast Imaging Reporting and Data System (BI-RADS) lexicon. For mass lesions, the three examination methods all evaluated the shape and margin. DM and DBT were used to evaluate the density of the mass, and US was used to evaluate the echogenicity, posterior feature and vascularity. The morphology and distribution were evaluated for isolated microcalcifications. The composition of mammary fibrous glands was evaluated according to BI-RADS lexicon. The molecular subtypes were defined according to the 2015 revised St. Gallen International Expert Consensus Recommendation. There were four molecular subtypes: luminal A, luminal B, HER2 enriched and triple-negative breast cancer (TNBC). Results: The lesions mostly showed as a palpable mass (89.9%), clinical T ₂ (50.4%), histological grade Ⅱ (58.3%), axillary lymph node metastasis (59.7%), luminal B type (44.6%), and BI-RADS were mostly 4 or 5 categories. Irregular shapes were the most common imaging features (P<0.001). In all examination, the luminal A type and TNBC type were mostly shown as mass alone lesions, luminal B was more common mass with microcalcification, and HER2 enriched type was mostly shown with microcalcifications alone lesions (P<0.001). Using both DM and DBT, negative diagnosis was more common in luminal A type tumors (P<0.001). For mass lesion, the most common findings on DM were indistinct margins (71.9%), whereas DBT detected spiculated margins (51.8%) which were related to luminal A type and luminal B type tumors (P<0.01). Benign morphological features on imaging may be correlated with TNBC type tumors, such as an oval or round shape (P<0.001) and circumscribed margin (P<0.01). The HER2 enriched type and TNBC type were larger than the luminal A type and luminal B type in the mass lesions (P=0.003). Conclusion: Some imaging features of breast cancer in young women ≤30 years old can be used to predict certain tumor molecular subtypes. The cancer detection rate of DBT was higher than that of DM, which has a wide application value for young women with dense breasts.

Key words: Breast cancer, Mammography, Tomosynthesis, Ultrasonography, Molecular subtype, Pathology