Tackling “Small” Breast Cancer in Ultrasonography: What Are They and Why Does Screening Them Help?

Background The study defined a group of “small” breast cancer (BC) detected at ultrasonography (US) and investigated the pathological nature of these small BC. We also explored factors associated with their recurrence and metastasis. Supplementary diagnosis with mammography was also considered. Methods This retrospective study included 491 BC patients pathologically confirmed with tumor size ≤ 10mm on US from January 2012 to December 2023; the study was approved by the institutional review board. We used chi-squared and unpaired independent t-tests to compare carcinoma in situ, including microinvasion (CIS) and invasive carcinoma regarding clinic, pathologic, US, and mammography characteristics. The characteristics associated with recurrence and metastasis were analyzed using univariate and multivariate Cox proportional hazard regression analysis. Results The analysis of 491 patients found that: for CIS, those with calcification were likely to be diagnosed by mammography (P < 0.001); for invasive cancers, those with unclear margins, irregular shapes and more color flow were likely to be diagnosed by US (all P < 0.005). 409 (83.9%) of the 491 patients received US follow-up with a median of 46 months. 17 of the 409 patients (4.2%) experienced recurrences, metastasis, or both. Women aged 40 years or younger and patients with invasive ductal carcinoma had the highest hazard rates for recurrence and metastasis (all P < 0.046). Conclusions For small BC, the sizes evaluated by US and pathology were partially in consistence. US diagnosis of invasive cancer had a relatively higher diagnostic rate, while mammography was advantageous in diagnosing CIS.