Background The additive value of dual-energy spectral computerized tomography (DESCT) in breast cancer imaging is still unknown. Purpose To investigate the role of DESCT in improving the conspicuity of primary breast cancer. Material and Methods Twenty-nine patients who were histopathologically diagnosed with breast cancer and underwent DESCT for staging of lung metastasis were evaluated retrospectively. The visual conspicuity of breast cancer was scored by two readers separately in reconstructed virtual monochromatic images obtained at 40, 60, 80, and 100 keV. A circular region of interest slightly smaller than the maximum contrasted portion of the primary breast cancer was manually placed. Iodine enhancement (HU) and iodine content (mg/mL) values of tumor, normal breast tissue and pectoral muscle, and contrast-to-noise values of images at four different energy levels were calculated. Results The lesion conspicuity score peaked at 40-keV series for both readers and was significantly higher than those at other energy levels (all P < 0.001). Lesion iodine enhancement was highest at 40-keV virtual monochromatic image reconstructions (P < 0.001). The iodine content was significantly higher in tumor than normal breast tissue, and pectoral muscle (P < 0.001). The highest contrast-to-noise value was obtained at 60 keV (4.0 +/- 2.5), followed by 40 keV (3.9 +/- 2.2), without a significant difference (P = 0.33). Conclusion The conspicuity of primary breast cancer was significantly higher in low keV virtual monochromatic images obtained by DESCT. This gives us hope that DESCT may play an effective role in detecting incidental breast lesions. It also raises the question of whether quantitative values obtained by DESCT can be used for characterization of primary breast lesion.