Intrinsic subtypes of breast cancers initially assessed as probably benign or of low suspicion on ultrasonography differ according to tumor size

OBJECTIVES: To investigate whether the intrinsic subtypes of breast cancers initially assessed as American College of Radiology Breast Imaging and Reporting System (BI-RADS) category 3 or 4a differ according to tumor size. METHODS: A total of 444 breast cancers in 439 patients initially assessed as BI-RADS 3 or 4a through ultrasound-guided core needle biopsy were included. Tumors were classified by the size criterion of 10 mm or smaller or larger than 10 mm and categorized as the luminal type (estrogen receptor [ER] positive and/or progesterone receptor [PR] positive and human epidermal growth factor receptor 2 [HER2] negative), HER2 type (HER2 positive regardless of ER or PR status), or triple-negative type (ER negative, PR negative, and HER2 negative). The relationships between tumor size and breast cancer intrinsic subtypes were analyzed. RESULTS: A total of 247 (55.6%) cancers were 10 mm or smaller, and 197 (44.4%) were larger than 10 mm. The luminal type was more frequently present in tumors of 10 mm or smaller (185 of 247 [74.9%]) than those larger than 10 mm (112 of 197 [56.9%]; P < .001). No significant difference was noted in the frequency of the HER2 type in tumors of 10 and mm smaller and those larger than 10 mm (27 of 247 [10.9%] versus 36 of 197 [18.3%]; P = .084). The triple-negative type was more frequently present in tumors larger than 10 mm than those of 10 mm or smaller (49 of /197 [24.9%] versus 35 of 247 [14.2%]; P = .012). CONCLUSIONS: Breast cancers assessed as BI-RADS category 3 or 4a had differing intrinsic subtypes according to tumor size, as the luminal type was more frequently present in tumors of 10 mm or smaller than those larger than 10 mm, whereas the triple-negative type was more frequently present in tumors larger than 10 mm.