Prediction of Metastasis in Small Pulmonary Oligonodules Detected in Breast Cancer Patients at Baseline <scp>CT</scp>

It is challenging for radiologists to diagnose pulmonary metastases when they encounter only a few (n ≤ 5) small pulmonary nodules (< 10 mm) on staging CT in breast cancer patients. We conducted this study to assess clinical and imaging features related to metastasis for better risk stratification. Retrospective analysis of 249 pulmonary nodules present at the baseline CTs of 194 patients diagnosed with breast cancer between 2014 and 2021 was performed. The evaluated features included nodular characteristics, perifissural nodules, associated imaging findings, clinical stage, and breast cancer subtype. Nodules with interval change were determined to be metastases. A large proportion of the patients had single nodule (78.9%) presence, and most of the nodules were less than 6 mm (86.3%). Among the 249 nodules, 63 (25.3%) nodules were in metastases. The independent predictors were nodule ≥ 6 mm, mediastinal/hilar lymphadenopathy, clinical Stages III and IV, and triple-negative breast cancer subtype. Nodules (≥ 6 mm) were assessed as weak evidence to rule in metastasis, and the results were as follows: positive likelihood ratio (+LR), 3.74; sensitivity, 30.2%; and specificity, 91.9%. With weak evidence of small pulmonary nodules (≧ 6 mm) to rule in metastases, it may be appropriate to follow the recommendations of growing nodule management. By contrast, the nodular shape, margin, location, perifissural nodules, and pleural tag did not show an association with metastasis.