Breast cancer ranks the second position among the cancer of women in Japan. We report two cases of breast cancer detected by 99mTc-tetrofosmin. First case was 51 years old female with breast cancer (invasive papillotubular carcinoma) and dextrocardia. She received 99mTc-tetrofosmin myocardial scintigraphy to evaluate dextrocardia and suspicious coronary artery disease. A planar image of 99mTc-tetrofosmin myocardial scintigraphy showed myocardium at the right side, gall bladder at the left lower side and abnormal uptake on the left chest wall. Transaxial images of 99mTc-tetrofosmin myocardial SPECT showed myocardium at the right side and abnormal uptake on the left chest wall. Second case was 78 years old female with breast cancer (intracystic papillary carcinoma) and arrhythmia. 99mTc-tetrofosmin myocardial scintigraphy was performed to evaluate arrhythmia and suspicious coronary artery disease. A planar image of 99mTc-tetrofosmin myocardial scintigraphy shows hot nodule at the lateral side of the myocardium. Transaxial images of 99mTc-tetrofosmin myocardial SPECT showed abnormal uptake at the left lateral side on the chest wall. Both cases appeared illed foci as abnormal uptake with 99mTc-tetrofosmin scintigraphy, although histological diagnosis was different. We conclude that 99mTc-tetrofosmin scintigraphy is helpful for evaluating breast cancer.